Construction and theory for everyone even/day tEP 7 7 ...

Construction and theory for everyone

even/day tEP 7 7electronics

low-cost easy to build useful al

This is

Stirling Sound's

price bombshell!

STIALINl3 SOUND

THE FACTORYorganised in the name of betterservice. Now our mail order dept.is right where the goods are made

THE SHOPreally 3 shops-audio showroom,component bargains, modules,etc. etc. Well worth a visit

NO

V.A.T. @ POSTAGE

Jll EMS

+ NEW DIRECT FROM FACTORY DELIVERY SPEED-UPAnother FIRST for Stirling Sound and 13-12-PWhy worry any more about working out V.A.T. (121% on £4.87 plus 8% on L3.39. plus85p for p/p, or should it be 54p?) We do it for you. Just send your order with the advertisedprices-we do the rest. The prices we give include V.A.T. at the appropriate rate and costof postage and package. Buy at our shop in person and we deduct the postage chargesautomatically. This is not all. Now you send your orders direct to our factory (see below)

ii where we make Stirling Sound products and send back your order from there even quicker-real time saving that! AND STIRLING SOUND PRICES REMAIN KEENLY COMPETITIVEALL THE TIME maintaining the lead we took in 1959 by being first in the U.K. to sell bargaincomponent packs. We've come a long way since then-with an exciting programme for theseventies we're going even further!

YOU PAY THE PRICE YOUREAD AND NOTHING MOREsubject only to (very rarely) there being a printingerror or really vicious price rise in production costs.You're SAFE when you buy from Stirling Sound-thebusiness that has grown on really understandingcustomers' needs and interests.

SPECIAL QUOTATIONS TO QUANTITY BUYERS.U.K. s6 OVERSEAS TRADE ENQUIRIES INVITED

BEST SELLERS 1N OUR 1977 RANGE OF Q.V MODULESThe Power AmpsSS.103 3 watt r.m.s. mono. Uses one I.C. pro-tected against short circuit L2.33S5.103-3 Stereo version of above using twoI.C.s L4.3355.105 5 watts r.m.s. into 3 ohms, using 12Vsupply £3.49SS.110 10 watts r.m.s. using 24V and 4 ohm load

E4 0555.120 20 watts r.m.s. into 4 ohms, using 34V

L4.61SS.I40 Delivers 40 watts R.M.S. into 4 ohmsusing 45 volts supply unit such as SS.345. Idealfor small disco, P.A. etc. L4.9955.1100 100 watts R.M.S. with heatsink mount-ing flange and built-in protection against short-circuiting L10-43SS. I 100/H As SS.I 100 but with full size heatsink

L11.82(Heatsink alone £1.39)

THE BARGAIN THEY ALL WANT!IT'S THE S5.1100 100 WATT R.M.S.AMPLIFIER MO 43) TOGETHER WITHSS.370 POWER UNIT (L14 63) plus full sizeheatsink for amp. (LI '39)You pay L24.25YOU SAVE £2.20 ! inc. VAT & pip(Items bought separately come to E26.45-seeabove)Your chance to lay the foundations of a reallypowerful disco or P.A assembly at a marvellousprice. This guaranteed Stirling Sound triumphis built for real hard work, so why pay more?

Tone Control andPre -amp ModulesSS.I00 Active stereo tone control, r, I 5dBon both bass and on treble L3.00S5.101 Stereo pre -amp for ceramic cartridges,etc. Passive tone control details supplied. E2.33SS.102 Stereo pre -amp for low output magneticP.Us. R.I.A.A. corrected. With circuit foradding passive tone control E4.04UNIT ONECombined pre -amp with active tone -controlcircuits. ± I 5dB at lOkHz treble and 30Hz bass.Stereo. Vol./balance/treble/bass. 200mV out for50mV in. Operates from 10 to 16V supply. E9.00UNIT TWOAs Unit One, but for magnetic pick-ups. Forinputs 1 to 5 mV per channel. R.I.A.A. corrected.Adaptable to ceramic. Designed to genuine hi-fistandards E12.43

The F.M. Tuning ModulesSS.201 Front end tuner, slow geared drive, twogang. A.F.C. facility. Tunes 88-108 MHz. L5-90SS.202 I.F. amplifier. Metering and A.F.C.facilities E3.46SS.203 Phase lock loop Stereo Decoder for usewith the FM mono tuners. A LED may be fitted

£419SS.203-1 Coil -type stereo decoder Neg. earthwith I.C. L3.06. 55.203-3 Pos. earth transistordecoder C250

Every effort is made to ensure correctnessin 'motion at time o oin to ress STIRLING SOUND DEPT. PW6,

37 VANGUARD WAY,SHOEBURYNESS, ESSEXTelephone-Shoeburyness (0702-28) 5543

8 POWER UNITSAT VERY COMPETITIVE PRICESFirstly, the range covers well over 65% of allconstructors' needs. Secondly, with 13-15 volttake off points on all models except SS.312, youget a valuable bonus; thirdly, the stabilisedmodels with variable outputs complete a rangeto suit almost all requirements.

S5.312 12V/IA L6-35SS.318 18V/IA E6.54SS.324 24V/ 1 A E72755.334 34V/2A E8.3155.345 45V/2A L9.9855.350 50V/2A E10-38SS.370 70V/2A E14.63

SS.310/50 Stabilised power supply with variableoutput from 10V to 50V/2A. Built-in protectionagainst shorting E16.69

SS.300 Power stabilising unit 10-50V adjustablefor adding to unstabilised supplies. Built-in pro-tection against shorting £502

GET MORE OUT OF YOUR CARwith a STIRLING SOUND "SUPER SPARK"Mk5 electronic ignition unit. Adjustable forpos. or neg. earth. Simple rev. limiting control;on -off imobilising switch; switch for instantrevert to normal ignition; neon indicator. Instrong, totally enclosed metal box 16cm x12cm x 10cm. 12 mths. guarantee.yam fete L1028 £1 2kitof pares cesced

SHOP AND SHOWROOM220-224 WEST ROAD, WESTCLIFF-ON-SEA,ESSEX SSO 9DFOpen all day Saturday

. EASY TO CONSTRUCT.SIMPLY EXPLAINED

VOL. 6 NO. 6 JUNE 1977

CONSTRUCTIONAL PROJECTSSIGHT AND SOUND FISH ATTRACTOR Arouses the curiosity of nearby fish by A. J. Bassett

DOOR CHIME INHIBITOR Only permits a single "ding-dong" by T. I. R. de Vaux-Balbirnie

TRANSISTOR LEAD OUT INDICATOR Identifies the connections to a transistor by A. F. Olivera

SOIL MOISTURE MONITOR Moisture content controls pitch of tone produced by J. Jenkins

MULTI -BAND TUNER Part 2 For receiving short, medium and longwave transmissions by F. G. Royer

GENERAL FEATURESEDITORIALSHOP TALK Component buying problems and new products by Brian Terrell

PLEASE TAKE NOTE Doing It Digitally, Instant Info.PHYSICS IS FUN Pitch and Volume by Derrick Daines

JACK PLUG AND FAMILY Cartoon

DOING IT DIGITALLY Part 9 Application of digital circuitry by 0. N. Bishop

FAULT FINDING Part 2 Simple amplifiers by Douglas Vere

FOR YOUR ENTERTAINMENT Intercoms and the Post Office by Adrian Hope

PROFESSOR ERNEST EVERSURE The Extraordinary Experiments of. by Anthony J. Bassett

BRIGHT IDEAS Readers' hints and tips

READERS' LETTERS Your news and views

DOWN TO EARTH Using old meters by George Hylton

BACK NUMBERS,LETTERS AND BINDERS

We are unable to supply back copies of Everyday Electron-ics or reprints of articles and cannot undertake to answerreaders' letters requesting modifications, designs or informa-tion on commercial equipment or subjects not published byus. An s.a.e. should be enclosed for a personal reply. Lettersconcerning published articles should be addressed to: TheEditor, those concerning advertisements to: The Advertise-ment Manager, at the address shown opposite.

Binders for volumes 1 to 6 (state which) are availablefor £2.10, including postage, from Post Sales Department,Lavington House, 25 Lavington St., London SE1 OPF

Don't miss ouPlace a

regulaorder

for ee TODA

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Everyday Electronics, June 1977 257

AMAMIBy A. J. BASSETT

I

THEREare many ways in which

fish may be attracted andcaught. Some ways are legal andsportsmanlike. Other methods areillegal, unsporting and in somecases so efficient that, in the handsof irresponsible persons theycould quickly clear our fishingplaces of stock and might, if un-controlled, even lead to the extinc-tion of whole species of fish.

One method which is illegal, butwhich might, paradoxically, beuseful in helping to conserve thefish stocks if it were correctlyused, involves passing electroniccurrents through the water inwhich the fish live. If a heavycurrent is used, the fish arestunned, paralysed or even killedby its effects.

If a weaker current is used ithas an effect on the muscles andnerves of the fish, causing them toswim towards one of the elec-trodes in a zombie -like manner.Most fish are unable to escapethis compulsion and are in effect,trapped the moment the currentbegins to flow in the water.

PRINCIPLES OF OPERATIONThe electronic fish attractor

described here is legal and sports-manlike; it does not cause elec-tronic current to flow in the wateror rely on anything illegal. Thefish are attracted, by their owncuriosity, to the vicinity of thedevice, and, having investigatedthe strange object, are free toswim away.

However, if a fisherman's hookis placed near the attractor witha suitable bait, the chances of acatch are definitely increased.The fish, having investigated theelectronic attractor and foundthat they cannot eat it, will bequite likely to take the bait. It'sthis element of chance, combinedwith the fact that the fishermanmust still exercise his skills inorder to land a catch, thatseparates this electronic fishattractor from other less sportingmethods.

Fish are naturally attracted bycertain sounds and repelled byothers. Low audio frequencies arefor most fish a danger sign fromwhich the fish will flee.

The clicking, buzzing and otherhigh-pitched sounds made byinsects and other potential preyare very attractive to fish, and asmall flashing light is also attrac-tive, especially at night or in adark pool. Many highly -effectivefish attractors have been made by

THE VERT IDEA

The idea for a Sight & Sound Fish

Attractor was proposed by a reader of

E.E. who receives oJr special award.

mechanical or electrical means toproduce similar sounds, or soundsin the same frequency range. Theuse of lights to attract fish,especially for night fishing, is alsowell known.

CIRCUIT DESCRIPTIONThe complete circuit diagram of

the Sight And Sound FishAttractor is shown in Fig. 1. Tran-sistors TR1, TR2 and associatedcomponents form a circuit calledan astable multivibrator (free -running square wave oscillator)which operates as follows.

When the circuit is switched on,both transistors attempt to turnon (become conducting) but dueto component tolerances, one willdraw current faster than theother. Say for argument's sakeTR1 turns on faster than TR2,then the voltage on the collectorof Till will become more positive,and this change will be fed back

FORGUIDANCEONLY ESTIMATED COSTOF COMPONENTS

excluding VAT.£3.00

excluding fishing lineand weights

Everyday Electronics, June 1977

DITIL 209

R3 1012

RI1700

+ -

C2 100pF

TR1AC -28

D2TIL 209

CI 100p

VRIR5 2200 100kI2

C3 inn/OFF

VR2100k!) R6 10512

TL1(SEE TEXT)

SiGRAVITYSWITCH

B1I -5V

Fig. I. Circuit diagram of the Sight and Sound Fish Attractor. Switch SI is a home constructed gravity switch.

to the base of TR2 via C2 and R4.A positive voltage on the base ofTR2 will cause TR2 collectorcurrent to fall thereby causingthe collector potential to movetowards the negative rail. Thisfalling negative voltage is fedback to the base of TR1 via Cland R3 causing TR1 to conductmore and in turn cause TR2 tomove towards a non conductingstate.

This regenerative action willcontinue until TR1 is completelyon and TR2 is off. Only one tran-sistor can be on at any one time.

Capacitor C2 now charges viaD2 and R4 until the charge onthe positive plate reaches asufficiently negative potential such

that TR2 starts to conduct andswitches hard on. We now havethe situation where TR2 is on andTR1 is off.

Since the collector voltage ofTR2 is at a low potential,capacitor Cl is free to charge viaD1 and R3. The capacitor incharging reduces the collectorcurrent of TR1 and increases thevoltage. This increase is fed backvia C2 and R4 to the base ofTR2, thus increasing the actionstill further. This continues untilsuch time as when TR1 is on andTR2 is off. The entire processcontinues in this way illuminatingthe l.e.d.s, each time the tran-sistors switch on and off, thusproducing the "sight" part of theattractor.

RED (FLASHING)

LOW FREQUENCYMULTIVIBRATOR

GREEN (FLASHING)

AUDIOOSCILLATOR

STEEL LID

MAGNETICEARPIECE

HOW IT WORKS

COCK

) CLICK

o -)41141,1004

The fish attractor comprises two oscillators. The first oscillatorruns at a low frequency about 1Hz and causes two I.e.d.s to flashon and off. The I.e.d.s have been chosen to be of different colours,one red, one green to enhance the effect.The second oscillator is set to produce an audible tone in themagnetic transducer attached to the lid of container holding theunit. The lid being of "magnetic" material oscillates in sympathy.To enhance the sound effect produced the output of the firstoscillator is used to modulate the second to produce both clicksand a varying audio tone.The resulting combination of lights and tone has a strange effecton fish, in which they find themselves attracted to the source, andhence the bait conveniently left there by the angler.

Components TR3, TR4 andassociated circuitry form a secondoscillator, this one being knownas a relaxation oscillator. Theprinciple of operation of this typeof oscillator is that capacitor C3 ischarged up to a pre -determinedvalue and then rapidly dischargedthrough the transistors TR3 andTR4 and this process repeated.

At the instant of switching on,capacitor C3 is discharged, hencethe emitter voltage of TR3 ismore positive than its base. There-fore no current flows in TR3 andremains non -conducting. As aresult no base current flows inTR4 and so this is also in a non-conducting state.

The capacitor begins to chargethrough TL1, VR2 and R6 and apoint is reached where the emitterof R3 becomes less positive thanthe base and TR3 starts to switchon (conduct). This allows TR4 basecurrent to flow i.e. TR4 begins toconduct. Because the collector/emitter resistance of TR4 has nowreduced slightly due to its con-duction, the potential on the baseof TR3 is made to rise causingTR3 to conduct more heavily,which in turn causes TR4 to con-duct more (reducing still furtherthe collector/emitter resistance).The end result is that both tran-sistors become saturated (turnedon fully).

The capacitor now starts to dis-charge through VR2, R6 and thecollector/emitter resistance ofTR4. As C3 discharges, TR3emitter potential rises and soreduces TR3 collector current andhence TR4 base current. Theresultant increase in the collector/emitter resistance of TR4 reducesthe potential on TR3 base therebyreducing collector current. This


clearly leads to both transistorsbeing fully off with the capacitordischarged. This chain of eventsis repeated for as long as thesupply is connected and producesan audible tone in TL1, thecollector load of TR4, forming the"sound" section of the attractor.

A modulated tone is producedin TL1 by coupling the output ofthe first oscillator to a voltagesensitive point in the secondoscillator, this point being theemitter of TR3.

The flash rate of the l.e.d.s maybe altered by changing the valuesof R1 and R2 or CI and C2,however the values of thesecapacitors determine the bright-ness of the I.e.d.s if they are de-creased to a very low value, thiswill result in an apparent loss ofbrightness.

By varying the resistance ofVR2, the basic frequency of therelaxation oscillator m a y bechanged, and by altering the valueof VR1, the modulating signal,which consists of a series ofsquare waves may also bechanged.

TRANSDUCERThe circuit may be installed in

a container such as a clear screw-top jar with a thin steel lid. Alow-cost magnetic transducercauses the steel lid to vibrate atthe frequency of the audio oscil-lator.

By this means the audio outputof the oscillator is coupled to thewater in the form of acousticwaves, Fig. 2a shows how thetransducer operates.

A horseshoe magnet carries acoil of wire, and a pulsatingcurrent through this coil causes asoft iron diaphragm to vibrate atthe frequency of the pulses.

A vast number of moving -d i a p h r a g m headphone -insertswere made for the Governmentand these are available at anumber of Government Surplusand electronic stores. The correcttype can be easily identified byunscrewing the cover, which re-veals the loose iron diaphragm.When this is removed the polesof the magnet can be seen. Thed.c. resistance of the coil isusually about 25 ohms.

Instead of using the iron dia-phragm which comes with theheadphones insert, place themagnet and coil assembly insidethe lid of the jar, so that the rimof the inset automatically spacesthe steel lid a little away from260

Components ,st) 1""um IN

ResistorsRI 470 S2R2 470R3 1052R4 1052R5 22052R6 I OkilR7 4.7k12R8 2.2k12R9 10t2All PN ± 10% carbon

PotentiometersVRI 1004(0 horizontal skeleton presetVR2 1001d1 horizontal skeleton preset

CapacitorsCI 100,uF elect. IOVC2 100,uF elect. 10VC3 10,uF elect. lOy

SemiconductorsTR I ACI28 germanium pnpTR2 ACI28 germanium pnpTR3 AC176 germanium npnTR4 ACI28 germanium pnpDI TIL209 light emitting diode (green)D2 TIL209 light emitting diode (red)D3 0A47 or similar germanium diode

MiscellaneousTL I magnetic transducer insert (see text)SI gravity switch (see text)BI 1.5V U7 batteryStripboard 0.1 inch matrix 10 strips x 21 holes; small plastic tube; small ball -bearing; washer; wide necked screw top jar; Blu-tak or plasticine asrequired; 18 s.w.g. or 20 s.w.g. soft steel wire (see text); fishing line, weightsas required; connecting wire; solder.

See

ShopTalk

page 263

the magnets, but the insert ismagneticaly stuck to the lid.Momentarily connect a 1.5 voltbattery to the coil. A loud clickshould be heard from the lid. Asmall quantity of adhesive maythen be used to attach the lid tothe rim of the insert. Do not usea lot of adhesive as this mayinterfere with the efficiency.

Alternatively, remove theplastic ear insert and the softiron diaphragm from a magnetictype radio or hearing -aid piece,and attach the magnet and coilassembly to the inside of the lid.In this case, there is usually acentral pole -piece, around whichthe coil is wound, surrounded byan outer circular magnet as shownin Fig. 2b.

GRAVITY SWITCHThe author considered a number

of methods of switching thecircuit on and off, without open-ing the jar, as it would disturbthe waterproof seal each time.Magnetic switches operated by

means of the influence of amagnet through the glass, wereconsidered, as was a mercuryswitch which proved successfulbut because the latter are notreadily available, a home-madegravity switch was devised usinga moving ball -bearing to makecontact.

The construction of the gravityswitch is shown in Fig. 3. A shortpiece of plastic tubing, and aball -bearing are chosen so thatthe ball -bearing is a loose fitinside the tube and will easilyroll about. Two small holes aredrilled opposite one another about3mm from one end of the tube,and into each hole is inserted abent piece of solid copper wire,so that when the ball -bearing fallsto this end of the tube, it bridgesboth pieces of wire and switchesthe circuit on.

A check is made to ensure thatthe ball -bearing makes andbreaks contact freely when thetube is tilted. The opposite end ofthe tube is then sealed by cement-ing in place a plastic disc or aEveryday Electronics, June 1977

SOFT IRON DIAPHRAGM

(a)

SOFT STEELBACK PLATE

COIL

CENTRE POLE PIECE (AROUNDWHICH THE COIL IS WOUND)

S

MAGNETICFERRITERING

SOFT IRON DIAPHRAGM

(b)

BI +ve

D

of

Fig. 2 (a) Illustrating the operation of a transducer.(b) A small earphone is usually constructed as in thediagram. For use in the Fish Attractor, the plasticinsert and diaphragm are removed.

END COVER

PLASTIC TUBE

BALL BEARING TR1,2,3 & 4UNDERSIDE VIEW

TWO CONTACT WIRES

!,)0 0 0 0 0 0 0 0.RI R2

R4

VR1

11141IL

,'+/R5

e ° C' 0 R3 0 e 0

0 0

TL1

0 0 0S1

r ID2 R6 0

aD3

TR1

C3

VR2e

e1123

b

R9

R

VP

O

O

O

O

b 0

R8 0 0 e 0 0

TR4

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0 o 0

O 00 o

o 00 I o

o o.O B o

0000000000oo0000oo

SPOT

Fig. 3. Construction of the gravity switch. Ensure thatthe ball bearing makes and breaks contact freely.

BI -ye

Fig. 4. Component layout on the stripboard, also show-ing the breaks required on the underside.

Photograph showing the completed circuit as built ona piece of stripboard.


suitably sized washer. This trapsthe ball -bearing in the tube andcompletes the construction of thegravity switch.

CONSTRUCTION ANDTESTING

The circuit is built on a pieceof 0.1 inch matrix stripboard size10 strips by 21 holes. The layoutof the components on the topsideand the breaks to be made alongthe copper strips on the under-side of the stripboard are shownin Fig. 4. The layout is not criticaland may be changed to suit re-quirements.

Begin by making the breaksand then positioning and solder-ing the resistors, capacitors,potentiometers and gravityswitch leaving the semiconductorsuntil last. It is recommended thata heatshunt be used on the leadsof the semiconductors when theseare being soldered in positionreducing the risk of thermaldamage from the hot solderingiron.

The magnetic earpiece trans-ducer is next connected to theboard by means of about 15cmof thin flexible twin wire, andthe battery connected by meansof short lengths of wire solderedto its terminals. If the battery isnot leakproof, it should bewrapped in several layers of blot-ting paper.

The circuit can now be tested.When the stripboard is held withthe component side upwards, thegravity switch should make con-tact, the l.e.d.s should begin toflash alternatively, and if thetransducer is placed in contactwith the lid of the jar, it shouldproduce a sound dependent uponthe setting of VR1 and VR2.

The sound can be varied froma series of clicks through a lowbuzz to a high pitched note, whichvaries in sympathy with the flash-ing of the l.e.d.s all of thesesounds appear to attract fish andthe degree of attraction dependsupon the type, age and size ofthe fish, among other factorswhich allow plenty of room forexperiment.

To install the circuit, use a widenecked screw top jar. Press alayer of Bostik-Blu-Tak orplasticine over the bottom of theinside of the jar, which must beclean and dry in order that thematerial will stick. It also helpsif both the jar and the materialare slightly warm. Use a quantity

sufficient to ensure that the jarwill float upright in water, butinsufficient to cause it to sinkwhen the circuit components andlid are added.

Press the circuit board andbattery lightly into the material,as in the photograph and securein place using several strips ofplasticine.

When satisfied that it is in work-ing order, and the gravity switchis functioning satisfactorily sealthe lid in place with a thin layerof Blu-Tak or other non -settingwater-resistant adhesive to act asa water resistant seal.

Although the lid should beeasily removable for adjustmentof VR1, VR2 and battery chang-ing, it is best not to open the jarvery frequently as this may re-quire frequent attention to thewater seal.

WIRE CASEPrepare a wire case for the jar

as shown in Fig. 5 using soft steelwire about 18 s.w.g. or 20 s.w.g.Suitable wire is often used forbinding parcels or packing cases,and this is best as it is treatedwith a rust -resistant coating.Alternatively thin birdcage wirecan be used, and is obtainablefrom some pet stores. Threefixing -loops are made, equallyaround the neck of the jar andconnected to a fourth loop under-neath.

Now the jar may be used with

DEPTH ADJUSTMENT -

Fig. 6a. Using a float and weight toposition the unit.

ADJUST DISTANCEFROM BOTTOM

FIXING RINGS

Fig. 5. Details of the wire cage.

a float and weight as seen inFig. 6a, or with a weight only asin Fig. 6b, as circumstances re-quire, together with a recoveryline for retrieval.

USING THE ATTRACTORWhen using the attractor with

a weight only, the length of linebetween the weight and theattractor will determine thedistance between the attractorand the bottom.

The breaking -strain of this lineshould be less than that of therecovery line, so that if the weightis caught by some underwaterobstacle, a heavy pull in the re-covery line will snap the thinnerline and allow the jar to floatfree.

A useful tip here, is that if afloat is also being used, and theweight is lost in this way and, ifby some misfortune the recoveryline also comes off, the attractorcan be recovered by casting inbetween the jar and the float.

Remembering too that for posi-tive sinking in salt water aheavier weight is needed than forfresh water, and that by tying acloth around the weight the jaris less liable to be broken.Good Fishing! I=1

WEIGHT

Fig. 6b. Positioning the unit using"bed"weight and own buoyancy.

262 Everyday Electronics, June 1977

CTRONIC SUPPLIES

By Brian TerrellNew products and component

buying for constructional projects.

AS FROM this issue I shall be writingthis column now that Mike Kenward

has departed, and will endeavour tomaintain the high standard of theservices of this page that you have beenaccustomed to in the past years.

Component PacksTwo packs of components arrived on

my desk last month, for my inspection,from Home Radio Ltd. One contained400 resistors with values in the E12range from 4.7 ohms to I megohm, allgold band tolerance (5 per cent) withwattages in the range to .1.W. Thispack designated SP22 costs £6 excludingV.A.T., making the cost per resistor

The other pack, No. C121 containedmany different types of capacitor andcovered an extensive range. There

The contents of the SP22 resistor pack.


were 30 electrolytics, 22 silver mica,20 paper/polyester and 32 ceramics,with values between I 5pF and 5000µF.The cost of this is £7 excluding V.A.T.giving a mean unit price of 7p. Thesepacks could make an economic startfor those wishing to build up a stock ofcomponents for project building.

Last MonthIn the May '77 issue we published

details for building a Remote ReadingThermometer which specified the use ofa 10mA d.c. meter. Some readers havefound difficulty in locating a meter ofthe type specified/used in the proto-type. Only more expensive types couldbe found. We see from advertisementsthat I mA types are more readilyavailable at less cost. These can be usedif fitted with a shunt resistor (RS) thevalue of this being determined fromRs = 0.11 x meter resistance (ohms).The minimum wattage required is

obtained from W = (0.009)2 x Rs watts.

Electronic Component KitThe Denshi electronic construction

kits now available from Electroni-KitLtd., (advertising in this issue) are idealfor those people who want to learnabout electronics but do not wish, ordo not feel competent enough tohandle a soldering iron, componentboard, wiring etc. The method employ-ed in this system is that of plug-incomponents encapsulated in trans-parent plastic boxes which are markedwith component symbol and value.

All kits are accompanied by manualswhich explain technical details ofprojects with diagrams and expla-nations.

The three kits available SR -3A(100 projects), SR-3ADX (105 projects)and SR-4ADX (150 projects) also in-clude basic electrical experiments andtheory such as Ohm's law, resistors inparallel and series etc.

Transistor Lead Out IndicatorThere should be no buying problems

encountered when buying componentsfor the Transistor Lead Out Indicator.The 3 -pole 6 -way switch seen in thephotograph is most difficult to locate,hence the Maka switch assemblyspecified-these are available frommany component suppliers. Some con-structors may be lucky enough to finda suitable type in a Governmentsurplus store and save themselves somecash as the Maka switches are costly.

Almost any miniature push-pull out-put transformer will do for the in-ductor, if not you have details for ahome-made version which will probablycall for a larger case than that listed.

Sight & Sound Fish AttractorOnly two components out of the

ordinary are called for in the Sight andSound Attroctor these being the magnetictransducer insert and the gravityswitch. The first component is dealt

with fully in the text and you have twoalternatives. If you are going to cutopen an earpiece, make sure that it'sthe magnetic type as this is the only onethat will work.

Mechanical details are given in thetext for constructing the gravityswitch. Instead a mercury switch can beused, a suitable type is available fromJ. Bull (Electrical) Ltd., 7 Park Street,Croydon, Surrey for a cost of £1.95including V.A.T. and post and packing.

Remaining ConstructionalProjects

Very few components are used in theremaining two constructional projectsthis month and all should be easilyobtainable. With regards the relay inthe Door Chime Inhibitor any type thatwill operate from a 9 volt battery andhas two sets of normally open contactsmay be used. Bear in mind that if a typeother than that specified is chosen, thewiring up on the component board willprobably need adjustment.

Bright IdeaAn American invention, known as a

Lightstick, is now available in the U.K.It provides up to 10 hours of lightwithout using batteries, flame, sparksor heat. The light is the result of achemical reaction contained in a 125mmlong plastic tube, activated by bendingthe tube.

It provides sufficient light in anaverage sized room for reading, tele-phoning, repairs, etc, and can alsobe used with complete safety inpotentially dangerous environmentswhere petrol and gas are about.

The light produced can be seen amile away; it is unaffected by adverseweather conditions and works under-water.

Generally available in the shopslater this year priced at £1.95 perpack of three, but at present onlyavailable from Tye Security Ltd.,Dolphin Road North, Sunbury -on -Thames, Middlesex.

A motorist putting a Lightstick togood use.

263

Only allotimes t

ne "ding dong" from your chime however manybell -push is operated during a preset period

THEOtOle unit to be dt*bed

wa,Ktfesigned to thve'ig theefforts et those bent oning thCOthor's sanity. T t: arevarious:; *vays of abusig doorchime#44.11 of them aXf#0)ng.Child*Cli sometimes gi# thebuttoreW*ery short press; 3Thatthe oft" part of the ing-dong" 'idly sounds, a heytend r#:.:4;lo this over a veragain..::A)Pe tradesman, lingrung of '< chimes and no ..eiv-ing attgf*mediate replydift.g. itagain,li:1#60 again. This ofthing f#::.paranteed to dist anysleepitfifWby.

Since door chimes ogkpudenough be heard with js one"ding4t*", the follow{"cir-cuit '''14evised to imp <thislimitatia00 It allows o

"ding-dong" no matter how thebutton is pressed. Further press-ing will give no results untilabout 20 seconds have elapsedand this time delay may be easilyvaried to suit individual require-ments.

THE CIRCUITThe circuit is shown in Fig. 1

and is seen to be hardly "elec-tronic" at all, in the sense thatthere are no active components.It consists of a general-purposerelay, which is an electro-mechanical component, a resistorof about 10 kilohms and anelectrolytic capacitor of about1,000 microfarads. Details of therelay are given later.

On pressing the bell -push, andthus closing the circuit, the relay

HOW IT WORKS;

BELLPUSH

r --

SOLENOID

L__

DECAYINGCONTROLVOLTAGE

ELECTROMECHANICALSWITCH

D 4

DOORCHIMES

On depressing the bell -push the chimes start to sound butfurther chime action is prevented by the electromechanicalswitch becoming open circuit. It is kept in this state by the derivedcontrol voltage. Further action of the bell -push has no effect.

After a while (about 20 seconds in the prototype) the controlvoltage decays to a level such that the switch is once again closed(rest position). This process is repeated next time the bell -push isoperated.

is energised and the capacitorbegins to charge up from the 9volt battery. This chargingcurrent falls off as the capacitorcharges and, typically, takes aboutone second for the relay to dropout into its original state.

The relay switches the chimesvia RLA2, one set of normally -open contacts, which remainclosed just long enough to givethe initial ding-dong. If this timeis too short or too long, a differentvalue of electrolytic capacitor canbe tried, or a different relay used.A higher value of capacitor willgive a long 'ding dong',while a smaller value will havea shortening effect.

CHARGE AND DISCHARGETIME

Further operation of the bell -push will fail to work the chimesbecause the capacitor will be leftin a charged state and cannot becharged further and so will notallow sufficient current to flow toenergise the relay. Under suchconditions the capacitor wouldtake a long time to dischargesufficiently to render the circuitoperational again and so aresistor of 10 kilohms is placedacross it. This allows the

FORGUIDANCEONLY 0.ESTIMATED COSTOF COMPONENTS *

excluding VAT.

£2.50excluding case


Fig. I. The complete circuit diagram of the Door Chime Inhibitor.

capacitor to discharge through theresistor in about 20 seconds.

If it is required to shorten orlengthen this time, a lower orhigher value resistor could beused, but a more flexible arrange.ment is to use a small presetvariable resistor of about 100kilohms which can be adjusted togive the desired time factor.

Another feature of the circuitis that even a very short press ofthe bell -push will give a full dingdong. This is because a secondset of normally -open contacts(RLA1) on the relay short cir-cuits the bell -push while the relayis energised.

OPERATION OF RELAYConstructors who have not pre-

viously used relays may find abrief description of their actionhelpful. A small current flowsthrough a coil consisting of manyturns of fine copper wire. Thiscoil is wound around a soft -ironcore so that as the current flowsit becomes energised and behavesas a magnet. Near the coil is anarmature which is attracted to itby the magnetic field and inmoving is caused to make orbreak various contacts which maybe used to switch circuits on oroff.

When the current is turned off,the magnetic field collapses anddue to spring action the armature


moves away to its original posi-tion, thus rendering the relaystatic again.

The simplest relays have onlyone normally -open or onenormally -closed set of contacts.Normally -open contacts willswitch a circuit on when the relaycoil carries current; normally -closed contacts will switch it off.Relays frequently have change-over contacts, which are a com-bination of normally -open andnormally -closed contacts.

CHOICE OF RELAYThe relay to be used for this

project should not have a coilwhich demands a high voltage foroperation. Some 'surplus' orcheap relays have 24V coils and,

although they may very well workon less than this, they are unlikelyto operate reliably from a 9Vsupply as specified here.

Some 12V relays may prove tobe suitable, but reliable operationis essential and they must bechecked by connecting their coilsto batteries, taking care to avoidtouching the bare connectionswith the hands. The rapid col-lapse of the magnetic field causesa high induced e.m.f. which can,on occasions, deliver an un-pleasant shock!

The relay chosen for the proto-type was a Doram type No 348-908, which has a coil resistance of185 ohms; coils with resistances ofmuch less than this are unsuit-able. This relay operates reliablyfrom about 6V upwards.

Components 9l'III-ft, ow

110

ResistorRI 10k0 PA/ carbon ± 10%

CapacitorC I 1000µF 10V elect.

SeeShoTali(

page 263Miscellaneous

RLA 9V 185 ohm relay with at least two sets of normally open contacts(Doram 348-908)81 9V type PP3Plain matrix board 0.1 inch pitch size 36 x 21 holes; p.c.b. type base to suitRLAI; Veropins; case to suit; battery clip to suit B I ; connecting wire; solder.

265

TO CHIMES/

0000000000O -yet

0 RELAY MOUNTING

o SOCKET

00 '000./7 RLA2 /

000O00 O

00RLA1

0 / 00 k+ e

R1

I I

,TO BELL -PUSH

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0OO

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

BATTERY /RETAININGWIRES

B100000

00

0000000000

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

® VERO PINS

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 000000000000000000000O R1 0O 0O 0O 0O 0O C1 00 0O 0O 0O 0O 0 0O 00 0O 0O 0O 0

001 0

00000000000000000000000000000000000000

_ TO BATTERY

Fig. 2. The layout of the components on the topside of the plain matrix board andthe interconnections on the underside.

The relay to be used must befitted with two sets of normally -open contacts. The 348-908 hastwo pairs of changeover contactswhich, of course, may be used asnormally -open contacts. If a relayis fitted with too many unusedcontacts, the mechanical com-plexity may render it slow andperhaps unreliable. The resource-ful constructor may take such arelay to pieces and remove anyunwanted contacts.

It was decided to power theprototype from a small 9 voltbattery mounted on the circuitpanel itself. Although a batteryclip is shown in the diagram, theconnections could be soldereddirectly to the terminals sincebattery life will be quite long. Itis possible to draw the power

from the batteries of the doorchimes themselves, if they arebattery operated, but if they arerun from a transformer then thetrouble of providing rectification

E

and smoothing would notworthwhile.

CONSTRUCTIONThe layout of the project is non-

critical, as the drawings of theprototype will reveal. Layoutdetails and wiring will dependlargely on the type of relay used.

When wiring up, however, besure to observe the polarity of theelectrolytic capacitor (the positiveend is marked + or will becolour coded; the negative end isconnected direct to the metalcasing). The capacitor shouldhave a working voltage in excess'of 9V and, although small 15Vtypes are available (and suitable),a 25V one was used in the proto-type because it happened to behandy.

The battery itself was securedto the matrix board by the simplebut effective method of using twoloops of wire to secure it in place.

The unit should be housed insome kind of small box, prefer-ably of wood. If a metal box isused, take care not to short cir-cuit any of the wiring.

CHECKING THE UNITBasic operation may be

checked, without connecting theunit to the chimes, by listening tothe clicking of the relay. Finalchecking, to ensure that it isworking as desired, will be madeby temporarily connecting it tothe chimes. To do this, the twobell -push wires should be brokenat some convenient point. Thebroken ends still leading to thebell -push are then connected tothe points marked X -X in the cir-cuit diagram (i.e. to RLA1 con-tacts) and the ends of the wiresleading to the chimes are con-nected to the points Y -Y (i.e. toRLA2 contacts).

Concerning Doing It Digitally Part 6, there isan error in Fig. 6.5 which gives details of atape reader. The "post" between the onesmarked "recorded" and "B" should read OVand not as printed. The diagram inFig. 7a is correct.

With reference to the Info. Chart presentedfree with the March '77 issue, there is a mistakein the capacitor colour code table. The "Tens/Units" column under "C280 Series andCeramics" should read the same as the "Tens/Units" column under "Tantalum Capacitors".


Physicsis FUN! By DERRICK DAINES

Pitch and VolumeTHE pitch of a note is entirely

dependent upon the number ofpressure waves reaching the ear in anysmall unit of time. This is termed itsfrequency, in the past expressed asc.o.s. (cycles per second) but nowadaysin hertz (contracted to Hz.) The termsare synonymous. The humming top isa familiar example but observerssometimes think that the sound is

getting louder when in fact it isgetting higher. They are not to bescorned for this since the human earis not too good at the differentiation atthe extremes of the hearing range,generally given as about 50Hz to about15,000Hz.

Readers with access to a variabletone generator can conduct a series ofexperiments on the acuity of theirfriends' hearing, but start with thegenerator giving a note outside therange of human hearing and ask themto raise a hand when they hear it andnot vice -versa, as sometimes a zealousparticipant will insist that he can stillhear the sound long after it has beenswitched off! It goes without sayingthat the speaker system used must beable to generate these very highfrequencies.

A reasonable substitute to a tonegenerator is afforded by a paint -stirring paddle in an electric drill thatis fitted with a variable -speed controlsee Fig. I. The drill is mounted in aframe and a springy flap of metal isarranged so that the paddle bladesstrike it. If the drill is run at full speed

Fig. I. A note is produced when a paintstirring paddle is struck against a

springy flap of metal.

the metal flap acting like a soundingboard will give off a note which is theproduct of the motor speed and thenumber of paddle blades. Slowing thedrill will lower the tone, lower andlower, until the individual beats willbe discernible.

Cardboard DiscsA toy suitable for children to play

with is made out of four discs oftough card, see Fig. 2. Cut them allthe same size with a radius of about10 to 12cm and pierce the centres with

a knitting needle. Now round thecircumference of the first disc markout 12 teeth equidistant. The othershave 24, 36 and 48 teeth respectively.Mount them on the knitting needlewith a slice of cork between each,secured with a dab of glue. The whole

Fig. 2. If a card is held against all fourdiscs, a chord is heard when theknitting needle is rotated.

arrangement may be spun by a smallelectric drill, driven by a clockworkmotor, or by some domestic appliancesuch as a food mixer.

A strip of postcard applied to eachdisc in turn will produce four differentnotes, while if a wider strip of card isallowed to touch all four at once apleasant chord is sounded. In fact, ifwe call the lowest notes the funda-mental, the others are the 2nd, 3rd and4th harmonics respectively. Incidentally,this tone -wheel system is the founda-tion of the Hammond organ sound.

In our cardboard toy all the discssound at roughly the same volume oramplitude. Were we to make a soundgenerator with a fundamental note and(say) all of the next 16 harmonics atequal volume, the result might not beall that pleasant since some harmonicsare not harmonious to the ear.

However, it is axiomatic that everymusical instrument sounds some har-monics louder than others and that asa general rule the higher harmonicsare softer than the lower. It is theblending of the various harmonics thatgives each instrument much of itstimbre or quality of sound.

JACk PLUG & FAMILY...DID YOU CONSTRUCT THEMODEL RAILWAY CONTROLLER?

YES, I DID. I CAN STARTAND RUN THE TRAIN AT ANEXCEPTIONALLY LOW SPEED.

(IT'S A UNIQUEPROJECT.

..SURELY BRITISHRAIL. HAVE BEEN USING IT

FOR YEARS.

.1111104111011.110..Everyday Electronics, June 1977 267

THIS MONTH we continue withmore projects illustrating the

uses to which digital circuits canbe put.

DIGITAL DICEA digital dice can be used in-stead of an ordinary cubical dicewhen playing many kinds ofgames-it is absolutely cheat -proof !

The dice uses a 7493 counterdriven by a clock working atseveral hundred (or even thou-sand) hertz. The circuit is shownin Fig. 9.1.

The counter starts at zero(0000) but when it gets to six(0110) the two outputs B and Cboth go high. These outputs arefed to a NAND gate, the output ofwhich immediately goes low. Thissignal is then inverted by anotherNAND gate giving a high whichresets the counter to zero.

The reset acts immediately thecounter gets to six so the actualsequence of counting is: 0-1-2-3-4-5-0-1-2-3-4-5-0 ... and so on.

By 0. N. Bishop

Use a slow clock to check thatthis really happens, but in actualuse a fast clock is necessary sothat it is impossible for anyonewatching to see what number thecounter has reached.

To stop the clock the switch isclosed, thus preventing pulsesreaching the counter and freezingit at what ever state it was in.If all lamps are at zero thisshould be counted as six, theother numbers being indicated bytheir binary equivalents.

Of course this is a very simpleform of dice yet it is cheat -proofbecause nobody can possiblyknow exactly when to press theswitch to score any particularnumber. Also the counter isoperating regularly so there isno bias towards any one numberal- there would be with a "loaded"dice.

It is also possible to designcircuits which will count fromone to six (instead of 0 to 5)and will also display the resulton a set of seven lamps arrangedlike the face of an ordinary dice.

LAMPS

Fig. 9.1. Circuit diagram of a simple digital dice. The throw of thedice is indicated on the lamps when the switch is closed.


00600000000000000000000000000000000000000000000600O 0O 0

00 I ,..1 0 * * 0 SOO

o

OIC2 o

O 7493 0

0 3 1 1

3,

3

* * wooog. I 0 0 oo *s 0 0 * 0 8 8 000 I, 0 0 * 0 0 0 oo 0 1111_9 * 0) 0 0 0 0 oO * * 0 * oo o

g * ***11 11:-/ galla 9

o 0o I 1 ft 0 0 o

oo o . 0 * * 0

o0

000 0

0

O0

7400CI 0

41'

* 0 'Ilii Ills ICli

. 0080

00

000

.

O

O11 4-6V o

0o o

OV FROM FROM oCLOCK SWITCH

O

00000000000000000000000000000000000000000000000000000

Fig. 9.2. Layout of the components for the digital dice on the experimental board.

Such circuits are more complexand the seven lamps add to theexpense. Several circuits havebeen published in this magazineso you could try making up oneof these for yourself or betterstill try designing one.

The layout for the Digital Diceexcluding the clock is shown inFig. 9.2. The clock can be con-structed around the third i.c.socket if it has not been madepermanent.

WHO WAS FIRST?The circuit shown in Fig. 9.3.

indicates which of two events

SWITCH A

SWITCH B

Ov

ICIJC2.7400

(DvFig. 9.3. Circuit diagram of the "Who Was First" unit.Switches A and B are normally closed. The lamp will indicatewhich switch was opened first.


happened first-even if one wasonly a millionth of a second be-fore the other. Logic circuits actquickly!

The two "events" are the open-ing of switch A and switch B.

It can be seen that the twoswitches are connected to twobistables via NAND gates. Eachbistable is connected to a lampto show which switch was openedfirst.

The circuit is first reset byclosing both switches and takingthe reset line low. Since a lowinput on either of the inputs toa NAND gate causes the output togo h.gh, this forces the outputs

LAMP 2

RESET

of gates ICla, IC1b and IC2d togo high. Both inputs to gates IC2aand IC2c will be high causingthe outputs of these gates to golow and the lamps to be off. Pro-viding the switches A and B arestill closed, the circuit will stayin this state when the reset lineis released.

Now supposing switch A is re-leased. Both inputs to ICla willbe high so pin 6 will go low thussetting the bistable in its otherstate-pin 11 high (lamp on) andpin 8 low. Since pin 8 is low,gate IC1b is effectively closed-operating switch B can have noeffect on the output of the gate.Thus A has blocked the actionof B.

Exactly the reverse situationoccurs if button B is releasedbefore A.

The circuit can be used whenplaying "snap" or some similargame to decide "who was first".

A pair of light -operatedswitches can be attached to thecircuit to see which of two modelracing cars wins a race. Thesego high in the dark so will givea brief high pulse as a car passesbetween the lamp and the photo-cell. A phototransistor circuit isrequired because of its fast res-ponse.

The layout on the experimentalboard is shown in Fig. 9.4. Theswitches used are those con-structed on the "keyboard" in anearlier part of this series.

A set-up for a race track isshown in Fig. 9.5.

0050000000000000000000000000000000000000CO0000

IC27400

1 it

r

oo 0

oo

S *

o7400o

o[I I 11 0 88 *

I

S 0

ICI

O 0O 0

00 O

8 8 :O B A RESET0 +6V 0O TO KEYBOARD

*

O **

LAMP 2

LAMP 1+

0 000000000000000000000000000000000000000000

Fig. 9.4. Layout of the components on the experimentalboard for the "Who Was First" circuit. The switches usedare those on the keyboard described earlier in the series.

LIGHT OPERATED TRACKSWITCH

LIGHT OPERATED SWITCH

TO CIRCUITBOARD

Fig. 9.5. By connecting light operated switches to the "WhoWas First" circuit and placing them as shown, the first car pastthe lamp can be indicated.

FLIP OR FLOP

The game "flip or flop" is justabout as difficult to play asnoughts and crosses and is likethat game in that after playingit a few times one never loses-except by making a mistake!

The game is based on the 7472flip flop. This i.c. has only oneflip flop inside it as comparedwith two in the 7473 but it ischeaper. The flip flop has threeeach J and K inputs, also a clearwhich sets the Q output low and

a preset which sets it high. Theseact independently of the state ofthe clock pulse.

The i.c. is shown connected upin Fig. 9.6. To play the gamestart with all the J and K inputslow (to ground) and ground theclear input for a moment so thatQ goes low and the lamp is out.

The two or more players playin turn. At each turn a playermust change any two of the in-puts. If, after he has done this,he thinks that the lamp willchange state when the clock in -

ow o o o o o o o o o o o oo o oo oo o oo o o oo o o o o o o o ooo0oo IC1o

qo

7472

o 44 371o

o CIII* 3 Io IIgo- 111

o 0 a

*0 0 40

"..40 44 a o 4 1 00o Io 0 : o o o I

0o 0 o 41 0 *00

SO 0 0 0 00o I

oo01, 0o 0 JCLEAR '---.'---' CLOCK W +6V

1o

.-......-,K

oo o o o o o o o o o o o o o o o o o o o o o o o o o o oo o o o o o o o o o o

LAMP I I)

p

9

Fig. 9.6. Layout of the wiring on the experimental boardthe "Flip Or Flop" game.

for

put is taken low he may groundthe clock input. If the lampchanges he wins a point if it doesnot then his opponent has thepoint. If the player does not wishto ground the clock line the turnpasses to the next player and nopoints are scored. The winner ofthe game is the first to score 20points.

This is not a difficult circuit tobuild permanently. Some varia-tions could also be incorporated.For instance, playing blind: In-stead of using toggle switcheswhere it is easy to tell the stateof each input just by looking atthe switch, use push -on, push -offswitches. This makes the gamealmost one of chance.

One could also play againstthe clock. Instead of having aclock button to ground the clockinput when a player thinks hecan change the state of a lamp,this version has a slow clockwith a period of about 0.2seconds. The player who is in themiddle of his turn or the playerwho has just completed his turnwhen the lamp changes scores apoint.

In this version one has theadditional feature of trying toget the inputs to the right stateat the right time. One could wirean extra lamp to show the stateof the lamp or one could justleave the players in the dark!

EGG TIMER ANDPHONE TIMER

The device to be described willtime short periods and light alamp or sound an alarm whenthe period is complete. There arelots of uses for this sort of devicein the home.

The circuit uses a clockoperating at about 0.2Hz, theoutput of which is connected toa 7493 counter. This will registerone count every five seconds sowill reach the full capacity ofthe counter in 75 (5 times 15)seconds. This may not be longenough for some applications butthe period can be extended inseveral ways. The count can bepassed first through a flip flopwhich will double the period, orthrough two flip flops which willextend the period to 300 secondsor five minutes (long enough foran egg timer).

The circuit with just the 7493is shown in Fig. 9.7. and withthe two extra flip flops in Fig.9.8.


14

2 13

7493 12

CLOCK 11

T=5 Secs.10

6 9

RESET

OV

OV OV

Fig. 9.7. A simple timer using a slow clock and acounter.

CLOCK5Secs.

2

3

4

5

6

0RESET\0.

0V

7

6V

7473

14

13

12

11

10

9

ComponentsDigital Dice74007493Clock circuitPush -to -make switch

Who Was First?7400 (2 off)Keyboard switches (2 off)

""ism IA)

Flip or Flop7472Push -to -make, push -to -break (8 off)

TimersClock: 7473 Alarm Unit: Rotary

7493 switch I -pole 5 -way74007440

OV 6V

Yz.TO PIN 147493

Fig. 9.8. The period of the counter may be extendedplacing two flip flops between the clock and the 7493.

The time is up when all theoutputs of the 7493 go high. Ifall outputs are fed to a four -inputNAND gate the output will stayhigh for five minutes then golow. This can be used to drive alamp or alarm.

If the counter keeps goingeven after the alarm has goneoff then the alarm will cease atthe next count. To overcome this,the output of the NAND gate could

CLOCKT. 5Secs.

CLOCK

1

CLOCK

2

7473

01

CLOCK

7493

C

50

TO LAMPOR ALARMSYSTEM

Fig. 9.10. Four two input and one four input NAND gatescan be used to give timing periods of one to five minutes asselected by a rotary switch.

be fed to a bistable which feedsthe alarm. This will then con-tinue sounding even when thecounter has gone back to zero.

The alarm can be made tosound after shorter periods thanthe full capacity of the counter.

Q2

7493

POWERSWITCH

A

C

CLOCK200 Hz

LOUDSPEAKERUNIT

LAMP

Fig. 9.9. The building blocks of a complete timer. The outputs of the 7493 can beconnected to any type of NAND gate and the output of the NAND gate can be con-nected to the bistable, the lamp or the loudspeaker alarm.


This can be achieved by usingonly some of the outputs of the7493 fed into a NAND gate. Forinstance if the A and B outputsare fed into a two -input NANDgate then the alarm will soundafter 60 seconds.

Thus the timer may be wiredup in several ways and Fig. 9.9.shows the complete system. Partsof this may be left out depend-ing on the application required.

Several NAND gates can bewired up if desired to give theoption of different timing periods.The outputs of the gates can betaken to a rotary switch as shownin Fig. 9.10. so that the switchselects the period.

As can be seen this is the sortof circuit which can be tailormade to specific requirements. Itis best to set it up on the cir-cuit board, play around with ituntil the desired results areachieved (learning a lot aboutlogic in the process) and thenbuild up the circuit permanently.

To be continued

271

I N ANCIENT China, it is said,I patients paid their doctors onlywhen they were healthy. It musthave given the doctors a greatincentive to cure diseases quickly!But it must also have raised a fewproblems. What is health? Untilyou know, it becomes hard todiagnose a disease.

It's the same with circuitry.Unless you know how a circuitshould work, you are unlikely tobe much good at diagnosingfaults. It may seem a tall orderto expect everybody to know howevery circuit works, in detail, justso that he can do a bit of fault-finding.

Fortunately it isn't necessary toknow anything like as much asthe chap who designs circuits. Ifhe is a competent designer, thenhe gets his component valuesright in the first place. The fault-finder only needs to know enoughto see where things have gonewrong. Another fortunate circum-stance is that the same types ofcircuit tend to repeat themselvesover and over again, in slightlymodified forms. Once you've gotthe hang of them fault-findingbecomes easy.

DEDUCTIONSKnowledge of the d.c. voltages

to be expected in a working cir-cuit is invaluable. If a particular272

By DOUGLAS VERE

PART TWO

Last month saw the introduction tofault finding, we continue by looking atone -transistor amplifiers.voltage is wrong, some componentor device associated with it isfaulty. But how do you know whatthe circuit voltages should be? It'smuch easier to make intelligentdeductions than you might think,because everybody, even thebeginner with only a knowledgeof Ohm's law and a general ideaof how a transistor works hasenough knowledge to do so.

We'll begin by looking at asimple single -stage transistoramplifier (Fig. 2.1a). This isan a.c. amplifier, as you can seeby the input and output capaci-tors, put there to block d.c. Sup-pose you have traced a fault tothis stage (by the signal -tracingmethods mentioned in the lastarticle), how can you identify theprecise cause of trouble? D.c.voltage checks are normally usedby repair men to do this. So whatshould the voltages be in a work-ing amplifier of this type?

To work, the transistor must beturned on. This means that basecurrent must flow in R1 and col-lector current in R2. In bothcases the flow is down from thepositive line (marked lice onmany diagrams, or with the actualvoltage).

The current flow in the tworesistances produces voltagedrops, and we can say, just bynoting these, various usefulthings. First, the collector must

be more positive than the base,because there is a drop acrossR1 which goes from collector tobase. Secondly, the collector mustbe less positive than the Vrr line,because of the drop in R2.

Fig. 2.1a. Single stage transistora.c. amplifier.

A third, perhaps less obviousfact .can also be deduced. Wheredoes the base current go afterentering the transistor? It canonly flow to the negative terminalof the battery. In doing so it mustset up a voltage drop across thebase -emitter junction of thetransistor, making the base morepositive than the emitter.

Even without knowing anythingabout the actual sizes of thesevoltages, you can still begin toEveryday Electronics, June 1977

fault -find with your voltmeter. If,on measurement, it turns out thatthe collector is less positive thanthe base, not more, as it shouldbe, then there's obviously some-thing amiss. (We'll discuss whatit might be later.)

EARTHHowever, it is much better to

get some idea of what the voltageshould be. Before looking intothat, let's just get one or twogeneral points straight. First, intransistor circuits it is usual toquote voltages with respect to thecommon side of the power supply.In npn circuits like this, thecommon side is normally thenegative battery line, and isnormally drawn at the bottom ofthe diagram. (In pnp circuits allthe voltages and current flows arereversed, but the principles arethe same.)

To measure a voltage in thisnpn circuit you connect thenegative terminal of the volt-meter to the negative batteryconnection and the positive volt-meter terminal to whatever pointin the circuit you are interestedin. By the way, the "common" sideof the circuit is often referred toas the "earthy" or "grounded"side. British technicians just callit "earth" (whether it is reallyconnected to the earth or not.)This is a convenient short way oftalking about it which I'll usefrom now on.

TRANSISTOR VOLTAGESWhere were we? Oh, yes, the

voltages. The base -emitter voltageof a working silicon transistor isusually in the range 0.5 to 0.9V(at room temperature). Thelower voltages are found whenthe transistor is passing only asmall current. To a roughapproximation, it's reasonable tosay that the base -emitter volt-age is 0.7V, and I'll do so fromnow on. (For germanium transis-tors a typical voltage is 0.25V,but the variation is much greaterthan for silicon, and it could beas low as 0.1V for a small audiotransistor.)

The only other voltage ofinterest is the collector voltage.There is no way of estimating itunless you know the d.c. currentamplification factor (hFE) of thetransistor.

In general, the circuit designerchooses resistances which set the

collector voltage to about half thesupply voltage, but variations maybe quite large. The collector volt-age is about half the supply volt-age when R1 is hFE times R2.Thus if Vec = 6V, R2 = 1kil andhFE = 100, the collector voltagewill be about 3V if RI = 100kfl.

Usually, in practice, hFE is notknown precisely. Transistormakers give it only between cer-tain limits (e.g. 100 to 300) anddesigners use average values.Since an individual transistor mayhave an hFE which differs quitesignificantly from the average, thecollector voltage may deviatesignificantly from what isexpected. Fortunately there is acertain degree of d.c. negativefeedback in the circuit whichhelps to reduce the effects of hFEvariations, but it can't eliminatethem. (The same applies to Fig.2.1b, where the emitter voltageis about half Vcc whenRI = hFE R2.)

A short way of referring to thed.c. voltages between the variouselectrodes of a transistor is towrite VBE for base -emitter volt-age, VcB for collector -base volt-age, VBE for collector -emittervoltage. If in Fig. 2.1a,VBE 0.2V instead of theexpected 0.7V you know eitherthat you are hot on the trail ofthe fault or that something hasgone wrong with the measure-ment! I'll deal with measurementerrors (caused by using an un-suitable voltmeter) later.

SHORTA common fault in transistors

is an internal "short" betweenbase and emitter. Often this not acomplete short but has enoughresistance to drop a small voltage.This could explain the 0-2V.Before unsoldering, the transistor,however, ask yourself what theleft-hand terminal of Cl is joinedto. It's just dangling in the airin Fig. 2.1a, of course, but in areal circuit it must be connectedto something.

If Cl has an internal short (or"leak" this could affect VBE. Forexample, if Cl (left hand) wereconnected to earth via a low valueresistance such as a 5 kilohmvolume control, then an internalshort could allow d.c. to flow inthe 5k volume control, robbing atransistor of base current andpulling down the base voltage. Aquick test checks this. Measurethe voltage at Cl (left hand). If

it's not zero, Cl is leaky.In other circuits Cl (l.h.) is

connected, not to an earthedresistance but to the collector ofa previous stage. In this case thel.h. side of Cl should be at avoltage above earth. A leaky Clthen allows current to flow fromthe previous stage collector TR1base. This augments the a.c. basecurrent and turns on TR1 harder,pulling down VcE, and perhapsto such a low value that TR1 canno longer work properly. (Withthis fault, VBE is raised slightly,but not necessarily enough todetect with a meter, unless youhave already measured it beforethe fault developed and notedexactly what it should be.

Fig. 2.1 b. Emitter follower stage,Note that the transistor "load"

is R2.

In the circuit shown in Fig. 2.1bthe transistor "load" R2 is in theemitter connection. This "emitterfollower" stage has an a.c. outputvoltage slightly less than thea.c. input voltage. Since the col-lector and base currents flow inR2, the emitter voltage is raisedabove earth voltage. If R1 is hFEtimes R2, the emitter voltage isabout half VEc. The base must bethe usual 0.7V more positive thanthe emitter, making the base -earthvoltage that much more positivethan the emitter -earth voltage.

POTENTIAL DIVIDE BIASThe simple circuit of Fig. 2.1c

uses what is often called "poten-tial divider bias". Here RI and R2,which are connected across thebattery, pass a current muchgreater than the base current ofTR1. As a result, the flow of basecurrent in RI, being so muchsmaller, makes little difference tothe voltage drop in Rl. Thusthe drop in R1, and thereforethe base voltage, is nearlyindependent of base current.


If R1 = R2, the base voltage(base to earth, that is), is halfVcc. 0 R1 is three times R2, thenthree-quarters of Vcc is droppedin R1 leaving one quarter acrossR2 and so the base voltage isVcc/4. In a word, RI and R2 forma potential divider which appliesa certain fraction of Vcc to thebase.

Suppose Vcc is 12V and RI =3 X R2 then the base -earth volt-age is 12/4 = 3V. The emittervoltage is about 0.7V less, i.e.2.3V. This 2.3V is across R4 andthe emitter current IE must there-fore be 2.3V/R4. If R4 = lkfl, /E=2.3mA. The collector current isvirtually the same, so if R3 is 2kilohms it drops 4.6V and the col-lector voltage must be about 7.4V.So if you know the resistances, thesupply voltage (Vcc) and VBE youcan make a fair estimate of allthe circuit voltages. Not a 100 percent accurate estimate, of course,but quite good enough to be ofuse in fault finding.

If the collector voltage ismeasured as 4V, for example, thisshould strike you as much toolow. Is a leaky Cl feeding currentto the base from the collector ofthe previous stage? Is C2 leakyand by-passing R4 to d.c.? Has aresistor changed value, or thetransistor developed a fault?Checking all the expected volt-ages in the circuit should help tolimit the possibilities.

Fig. 2.1c. In this circuit "potentialdivider bias" is used, as explained

in the text.

OVERLOADING PROBLEMSIncidentally, there is one quite

common fault which can throwout all the circuit voltages eventhough every component in thecircuit is perfect. This fault is"overloading" of the transistor byvery strong signals. Quite often,the signals get there by accident.

For example, an audio amplifiermay, because of accidentalcoupling between output andinput, burst into radio frequencyoscillation. You hear nothing(except perhaps a loud hiss) inthe speaker, but the strongoscillations upset the voltages(and may easily wreck thetransistors).

SHUNTSA small piece of auxiliary

equipment takes care of the prob-lem, temporarily. It is a genuinebit of test gear in its own right,though not often referred to inthe textbooks. It's just a capacitor,of 100nF (0.1p.F) or more,fitted with flexible leads whichterminate in crocodile clips. Onelead is clipped to earth. The otheris attached to points in the circuitwhere the unwanted oscillationsmay be present-say the collectorsor bases of transistors.

The impedance of 100nF toradio frequencies is low, usuallylow enough to short the r.f. toearth and so stop the oscillation.The transistor voltages shouldthen return to normal, if thetransistors have not beendamaged.

In some circuits, especiallyradio receivers, the mere act ofconnecting a voltmeter to a pointin the signal path may causeoscillation, and in such circuits itis a wise precaution to connectthe "shunt capacitor" (I'll call itthat in future) before starting totest.

In audio circuits, connecting ameter to a sensitive amplifier mayaccidentally introduce strong"hum" which upsets the d.c. con-ditions. To bypass the hum (whichis at the mains frequency, a lowfrequency) a large shunt capaci-tance is required. Whereas the100nF can with advantage be ametallised foil type, its largerhum -shorting brother willprobably have to be an electro-lytic, because in large capaci-tances these are so much cheaper.

In this case, remember to get thepolarity right. And, in both cases,make sure that the working volt-age is at least as high as lice. Areasonable "hum shunt" would belOpF, 64V working. This will suitmost circuits.

In theory, 10,11F should performequally efficiently both as a humshunt and an oscillation stopper.However, theory is misleading.The impedance of electrolyticcapacitors does not go on fallingas the frequency is increased, as itshould, but starts to rise againsomewhere above the audiorange. So at, say, 10MHz, your10/1F electrolytic may have amuch higher impedance thanyour 100nF metallised foil, andbe less effective as a shunt to h.f.signals.

If you have an assortment ofcapacitors, and two double endedcroc-clip leads, you can, of course,lash up shunt capacitors as theoccasion arises, and try outdifferent ones on the spot.

CIRCUITRYTo return to our circuitry.

We've now looked at somecommon types of single -stageamplifier, and indicated the cir-cuit voltages, or at least how toestimate them. Practical transistorcircuits seldom fall neatly intoone of these categories. Designersmodify them or use combinationsof them to suit their purposes.

For example, a designer mayput a resistance in the emitterlead of Fig. 2.1a. This has theeffect of increasing the inputimpedance and reducing distor-tion at the expense of gain. Thecircuit is then a sort of hybridbetween Figs. 2.1a and 2.1b. Thenagain, two or more transistorsmay be direct -coupled, with thecollector of one stage connecteddirectly to the base of the next.This is a common arrangementin audio power amplifiers. We'lllook at one of these multi -transistor combinations later.

To be continued

Ask yourself what the left-hand terminalof CI is joined to.


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MomPhone/Door BELL REPEATER

An electronic bell -extension system.

...FUZZTONEunn

More than just a fuzzbox!! This unit, built ina robust case, allowscomplete control of toneto be obtained. Has bothcut and boost of trebleand bass frequencies.

everydayelectronics

JULY ISSUEON SALEFRIDAYJUNE 17


PNP e e b

b c e

b e c

e c b

CONTINUITY TEST

FORGUIDANCEONLY g

ESTIMATED COSTOF COMPONENTS

excluding VAT.

5.00excluding case

TRANSISTORLEAD OUT INDICATOR

ALi, electronics constructors,from the professional to the

occasional dabbler, find that overa period of time a homogenouscollection of electronic bits andpieces is amassed, which in-variably includes a large numberof transistors. Many of these willhave had their markings rubbedoff, while others may bear anunidentifiable code number.

It is possible with the aid of amultimeter to identify the lead -outs of unknown transistors, butthe process is very tedious andone is never very sure of theresults.

With the unit described in thisarticle, however, the lead -outs ofbipolar transistors can be identi-fied in a couple of seconds, whichis just what is required by thosewho invest in semiconductorpacks containing unmarked anduntested transistors.

The indicator will also identifythe transistor as pnp or npn, con-firm that the transistor is service-able, and as a fringe benefitserves as a very useful audiblecontinuity tester.

It will not, however, work withfield effect or unijunction tran-sistors.

THE CIRCUITThe complete circuit diagram

of the indicator is shown in Fig.1. The heart of the indicator isa Hartley oscillator. If the col-

lector, base and emitter of a tran-sistor are connected to c, h and erespectively the circuit will oscil-late and a tone will be producedby the loudspeaker.

If therefore an unknown tran-sistor is connected to the oscil-lator via a switch capable ofselecting all possible combina-tions of the transistor's threeleads, a tone from the loud-speaker will indicate that thecorrect combination has been

made; the switch position canthen identify the three leads.

While this switching is beingcarried out the full supply vol-tage is applied across the transis-tor's terminals in all possiblecombinations, and to avoid break-down of the semiconductor junc-tions this voltage has to be keptto the minimum. In the event,tests revealed that a supply vol-tage of 1.5 volts was sufficientfor a very adequate signal to be

TRANSISTORUNDER TEST

MULTI -WAYSWITCH

111:1111

HOW IT WORKS

OSCILLATOR

OUTPUT AUDIBLELOUDSPEAKER TONE

I I

The circuit of the Transistor Lead Out Indicator is an oscillatormade complete by the insertion of a transistor (the one undertest). Being a 3 -lead device, the transistor can be connected incircuit in six different ways. This is accomplished by means ofthe multi -position switch. For only one position of the switchdoes the device oscillate and produce an audible tone in theloudspeaker. (Some transistors may produce a tone when c ande are transposed, but with less intensity.)


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LS1800

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131

1.5V 100

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03

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0506

02

03

04 Sib

0506

02

03

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P-1--cxST

I SOCKET

4 Slc

0506

Fig. I. Circuit diagram of the Transistor Lead Out Indicator.

produced. Some transistors gavea stronger output than others,but in all cases the tone wasclearly audible.

Resistor RI provides base biasfor the transistor under test,while the positive feedback pathis through Cl; C3 couples theoutput to the loudspeaker. It isimportant that the ground con-nection of the loudspeaker bebrought to the supply side of S2:this ensures that the negativeterminal of electrolytic capacitorC3 is correctly connected what-ever the position of S2. WhenS2 is in the pnp position the loud-speaker ground connection ismade through the dry cell.


The frequency at which theunit oscillates is governed by C2and the inductance of Ll, butit is also affected by Cl. It wasfound that the frequency variedwith different transistors-sometransistors in fact oscillated atnear supersonic frequencies. Theunit had therefore to be de-signed to oscillate at as low afrequency as feasible, and thevalues quoted for Cl and C2 werefound to be the most suitablefor the coil used in the prototype.

INDUCTORThis coil in the prototype was

a miniature push-pull output

transformer filched from an un-serviceable transistor radio.Various types from the sparesbox were tried and all workedwith varying degrees of efficiency.Only the primary (i.e. the wind-ing with three connections) isused. The two leads from theother winding may be used toanchor the transformer in place,but must be electrically isolatedfrom the rest of the circuit.

A home -constructed coil wasalso tried, with excellent results.For those who may be interesteda suitable coil can be made bypile -winding 600 turns of 30 to40 s.w.g. enamelled copper wireon to a piece of 9mm (38in.) fer-rite rod about 70mm long. Acentre -tap must be drawn out at300 turns, see Fig. 2.

Switch S1 used on the proto-type was a rotary 3 -pole 6 -waytype. It may be difficult to obtaina ready-made switch of thisspecification but one can veryeasily be assembled from "Maka-Switch" parts by using two 2 -pole 6 -way wafers, one of thepoles being surplus.

The switching circuit is shownin Fig. 3 and is drawn using two2 -pole 6 -way wafers as men-tioned above. This looks rathercomplicated mainly because ofthe cross -connections involved;constructors may find it easierto make up the connections byfollowing the switch positiontable.

Socket SKI is a miniature 2.5or 3.5mm jack socket with built-in switch, and provides the conti-nuity testing function of the unit.A pair of prods are connectedto a suitable jack plug, see Fig.3: when this is inserted into thesocket the built-in switch inter-rupts the supply, which is onlyrestored when a short-circuit ispresented to the prod ends.

Readers will notice that no on/off switch has been incorporatedin the design. There is no needfor one because the supply isalways interrupted when thereis no transistor in the test termi-nals and when the jack plug isinserted in its socket (provided,of course, the prods are notshorted!).

CONSTRUCTIONThe prototype was built into

a wooden case measuring 180 x83 x 48mm. The sides werecovered with laminate simulatingwood veneer, and the lid with

277

70mm

#111POPER9R.r,ROD

Cj1 RI; RA;ITSATPE rOOUPT

Fig. 2. Construction of the alternative coil, whichmay be used in place of the push-pull transformer.

Fig. 3. Diagram showing thestripboard layout, with thebreaks shown on the under-side. Also shown is thewiring details for the 2 pole6 way switches, and theconnectors required on thefront panel.

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Components 5131ont 111)

ResistorR 1 10k CI PA/ carbon ± 10%

CapacitorsCI 0.22µF plastic or ceramicC2 0. leF plastic or ceramicC3 .5uF 3V elect.

MiscellaneousSI 3 -pole 6 -way rotary switch (see text)S2 2 -pole 2 -way toggle switchSKI 2.5 or 3-5mm switched jack socketSK2 three -pin transistor socketL 1 miniature push-pull output transformer or home made inductor-

see textLSI 80 ohm miniature loudspeaker approx. 60mm diameter81 I .5V type U7 or similarStripboard 0. I5inch matrix 8 strips x 13 holes; Terry clip for 81; knob withpointer; jack plug to suit SKI; crocodile clips (2 off); case-prototype size180 x 83 x 48mm; connecting wire.

See

ShoTab(

page 263

white laminate. All the compo-nents were mounted on the lid,as can be seen in Fig. 3 andphotograph. The layout and wir-ing of the various components isnot critical and constructors mayif they so wish adopt a differentlayout.

The dry cell, Bl, is held inplace by a Terry clip, the supplyconnections being soldered to thecell's terminals. Current consump-tion when the unit is in use isin the region of 2 milliamps, andsince use is not continuous itshould be a very long time be-fore the cell has to be replaced.

The layout of the componentson the stripboard and the breaksto be made on the underside areshown in Fig. 3. Begin by mount-ing the components on the pre-pared board as shown and thenprepare the lid of the case toaccept Si, S2, SK1 and SK2. Thefront panel (lid) can be drilledwith a series of holes imme-diately above the location of theloudspeaker cone, or a suitablysized hole backed with speakerfret will do.

With all the components inposition wiring up should be car-ried out according to Fig. 3. Thecomponent board was mountedon an aluminium bracket andpositioned over the loudspeakerwhich was held in place with afew dabs of Evostik.

The panel lettering was madewith Letraset transfers, whichgive a very professional effect.After lettering the face of thepanel should be coated with aclear varnish (preferably matt)to protect it.


tone is heard, S2 (pnp/npn selec-tor) is changed over and S1 againrotated until a signal is heard.The pointer on the knob of S1will then indicate the identity ofeach of the transistor's terminals,and S2 the polarity of the device.

With some transistors the unitwill oscillate in two positions ofS1 i.e. with the emitter and col-lector transposed. In these casesthere is usually a stronger out-put at the position correspondingto the correct terminals. In anycase the base terminal will alwaysbe correctly indicated.

To use the unit as an audiblecontinuity tester a transistor hasto be inserted and the unitadjusted until a tone is produced.The jack plug is then put inplace and the tone will thensound only when the prods are

Photograph showing how the components are mounted on the lid.

USING THE INDICATORThe indicator is extremely

simple to use. The unknowntransistor is inserted in the tran-sistor holder and S1 rotatedthrough its six positions; if no

shorted. In practice the presenceof a resistance of a few ohmsbetween the prods still producesa tone: there should be no con-fusion however because the pitchof the tone changes noticeably.L1

279

ALMOST everyone has a love/haterelationship with their telephone.

Recently the British Post Office made agesture that should engender a littlemore love. We all know it costs con-siderably more to place a call throughan operator than to dial it direct. Butuntil recently this extra charge waslevied even where the subscriber hadonly called the operator out of despera-tion, for instance, because directdialling had produced wrong numbersor dead or crossed lines.

This surely made the Post Office oneof the only firms that penalised custom-ers for its own mistakes! But now aconcession has been made, and if a

call fails the operator will connect youat around the cost of dialling direct.

Incidentally, it isn't an old wives' talethat calls fail and the phones always gowrong in wet weather. It's fact.Because our skylines are now largelyclear of telephone lines (think whenyou last saw a telephone pole, and itmay surprise you), virtually all ourphone cables run in channels under-ground. And, quite simply, when itrains the channels fill up with water,the wires get wet and circuits short.It's as simple as that; but you'd besurprised how many people don'trealise it.

Interference ProblemsA reader wrote recently asking if

there were any steps one can take tominimise the interference one gets ona.m. mains intercoms, i.e. wireless in-tercoms. Because he was thoughtfulenough to enclose a stamped addressedenvelope, I promptly wrote back, butwith the depressing news that there isreally absolutely nothing one can do.

As we have previously reported themains is now horribly cluttered withaudio interference, as generated bythermostats, fluorescent lights andworst of all thyristor dimmers. As a

280

By ADRIAN HOPE

result a.m. intercoms, which use themains as their audio frequency linkbetween station and station, areinevitably terribly noise -prone. Thingsgot so bad in the USA that f.m.(frequency modulation) rather thana.m. (amplitude modulation) intercomsare now available, and at least onemodel is now sold in this country.The cost is high, over £40 a pair.However, because virtually all mains -borne interference is a.m. rather thanf.m., they can provide virtually noise -free communication, just as f.m. radioreception is virtually immune frommost forms of interference.

Money In Your PocketWith Post Office rental charges

continually rising, it is opportune torecall how one can quite legally cutPost Office costs in a small businesssituation by using these instruments.Consider, for instance, boss in oneroom and secretary in another. Ideallyboth have a telephone extension, butthe secretary has one of the type whichenables her to receive calls, talk toboss, and selectively route callsthrough. But of course these (the PostOffice call them Plan 107 installations)cost more to rent than ordinaryextension phones. What you doinstead is have ordinary extensionphones in each room, with the boss'sphone equipped with the standardPost Office switch to enable its bellto be silenced. You also have a pair off.m. wireless intercoms, one in eachroom. The crucial point, often over-looked, is that when a telephonereceives an incoming call it can betemporarily hung up without dis-connecting that call. So when secretaryreceives an incoming call, she simplysays "hold on", hangs up her phoneand buzzes through and talks to bosson the wireless intercom to advise himof the call.

Boss then either picks up hisextension phone or asks secretary topick up hers again and deal with thecall. What the secretary must never dois hang up her phone on an outgoing callbefore boss has picked up his, becausethis will disconnect it.

At current Post Office prices, yousave £17.60 per year on phone rentalby adopting this simple approach!All we need now is for an enterprisingBritish electronics firm to produce acheap and reliable f.m. wirelessintercom. (Certain regulations governthe use of a.c. mains intercoms, and theLocal Electricity Area Board should beconsulted before installing such instru-ments.-Ed.)

RegulationsFinally, although the Post Office

regulations may seem irksome toanyone encountering them they arefounded on sound common sense.For instance, it seems highly irritatingthat the Post Office insists on answeringmachines being connected by only afew approved firms who are willing toobserve rigid technical specifications.One such requirement is that anautomatic gain control must be builtinto the answering machine recordcircuitry, so that it will ignore anysignal more than 35dB below theI volt reference level and disconnectthe machine from the telephone linealtogether if this minimum thresholdlevel is not reached again after I0seconds.

This, of course, increases the priceof a machine; but is also means that nolow-level conversations, which mayresult from crosstalk between un-related lines, can be recorded. Thinkof the number of times that you haveheard faint conversations in thebackground to your own call equatethat with the number of times yourown conversations must interfere withother calls, and be thankful thatlegitimately installed recording mach-ines won't be able to record them.

"A computer made Nigel redundant-ittook up all his office space."


FORGUIDANCEONLY ESTIMATED COSTOF COMPONENTS

excluding VAT.

£2.50excluding case

FOR many amateur gardeners,the watering of plants is a

rather sporadic affair, dependingon luck rather than judgementwhen they actually are watered.For optimum results, however, itis necessary to know how wet thesoil is at root level, and to areasonable degree of accuracy.

Obviously, some sort of gadgetis needed which can display thisinformation in a clear and directway. A design to do just this waspublished in E.E., March 1975. Itused the principle that the mois-ture of the soil is proportionalto its resistance. Using one tran-sistor in an emitter follower con-figuration, a light emitting diodewas made to light up, its bright-ness being proportional to theresistance between two probesinserted into the earth

In theory, this circuit is excel-lent, and has the advantage ofbeing cheap and simple Its limita-tion, however, lies in the use ofa light emitting diode to displaythe information. There is notvery much difference between,say an l.e.d. which is at 40 percent of its potential brightness,and one which is at 50 per cent.The use of a visual methodmeans that the ambient lightingcan make results seem mislead-ing; in bright sunlight, the 1.e.d.might seem to be almost off,while in subdued lighting, itmight seem quite bright, eventhough the current flowing

through the diode in the twocases was the same.

The author decided to try toimprove the situation and toyedwith the idea of using an am-meter to display the current flow-ing, but this idea was abandoned,mainly because of the high costof meters. Instead the followingdesign was evolved.

The controlling factor is theresistance of the soil betweentwo probes, but the indication isthrough a loudspeaker, whichemits a loud clicking noise whena circuit is made between twoprobes; the rate of clicking isdependent on the resistance be-tween the probes.

CIRCUIT DESCRIPTIONThe circuit diagram of the

Soil Moisture Monitor is shownin Fig. 1. It is in fact a relaxationoscillator. Its advantages over astandard multivibrator are thatit only needs one capacitor, andit can be made to have long offperiods, and short on periods,thus cutting down on currentconsumption.

When the voltage is appliedto the circuit, capacitor Cl beginsto charge up. The base of TR1,which is an npn type is almostat negative supply potential. Itbegins to get more and more posi-tive as the capacitor charges upuntil it begins to conduct. Tran-sistor TR2 now begins to charge

HOW IT WORKS

OSCILLATOR

PROBE

SOIL "RESISTOR"

.1

I I II (DRY)

111111111111moisT)OUTPUTLOUDSPEAKER

The Soil Moisture Monitor consists of an oscillator with acomponent missing-a resistor. This resistor is vital for theoscillator to work and its ohmic value determines the frequencyof oscillation. This "resistor" is the d.c. resistance between twospecified points in the soil and is brought into circuit by means ofthe probes inserted in the plant pot, usually to root level.

Moist earth has a lower resistance than dry earth so the outputfrequency (heard in the loudspeaker) will indicate the dampnessof the earth in the vicinity of the probe tips.

LS1an

Cl 22pF

{PROBES1

TR1BC109

RI 3.3k/1

Wv

a, 5V "I

b TR2AC126

Fig. I. The circuit diagram of the Soil Moisture Monitor.

up until it too conducts. At thispoint, a current is passed throughLS1. The voltage on the collec-tor of TR2 now becomes morepositive, discharging Cl, andstarting the whole process again.

The rate at which this all hap-pens depends on how quicklythe capacitor can charge up, andits value. The former dependson the resistance between theprobes, together with R1 inseries with it.

It was found that almost anyspecies of transistor will functionin this circuit, the only criticalfactor being that one must benpn and the other pnp. The twonamed in the component list werechosen because of their cheap-ness and ready availability.

Soil resistance is typically100,000 ohms and 2,000 ohmsranging from completely dry tosaturated, and so the componentvalues have been chosen to givebetween 3 clicks per second, andone click every 3 seconds.

CONSTRUCTIONThe unit was constructed on a

small piece of 0.1in. stripboard,measuring 18 holes x 10 strips.The board, with components isshown in Fig. 2. Capacitor Cl ismounted upright on the board,taking note of the connections.The lead out connections to thetwo transistors are shown. Theseshould be noted, as the two aredifferent.

Just about any case could beused to house the project. An oldtobacco tin covered with Fablonwas used to house the prototype,but some will prefer the rathermore conventional aluminiumcases available. It is a good ideato put a piece of foam rubberin the box, to stop the batteryrattling inside. Holes must bedrilled to accommodate theswitch, and for the leads to theprobes. If a metal case is used,it is a good idea to have a rub-ber grommet on the hole to stopthe wires rubbing against themetal. Holes must also be drilledto allow the sound to escapefrom the speaker.

PROBES

Details for constructing theprobes are given in Fig. 2.Although the dimensions givenare not absolutely critical, it isa good idea to stick reasonablyclose to them. They are con-structed from strong aluminium.

Components au 114

ResistorRI 3.3k0 PN 10% carbon

CapacitorCI 220F 10V elect.

SemiconductorsTR I BC109 silicon npnTR2. ACI26 germanium pnp page 263

MiscellaneousSI d.p.d.t. slide switchLS I 8 ohms miniature loudspeaker approx. 56mm roundBI I -5V U7 batteryStripboard 0.1 inch matrix 18 holes by 10 strips; small aluminium case;grommet; connecting wire; insulation tape; wood for probes 25mm x 40mm x15mm; aluminium 100mm x 15mm 14 s.w.g. (2 off); No. 8 round head screws(4 off).

See

TAIK


0 0 0 0 0 0 0 0 X00

TR1 TR2UNDERSIDE VIEW

INSULATION TAPE

ALUMINIUM

Fig. 2. Layout of the components within the case and complete wiring up

The easiest way to cut this iswith a hacksaw, and then filingdown the rough edges.

The aluminium is covered withinsulation tape, except for theextreme ends. Care should betaken that the screws whichsecure the .metal do not touchinside the wood, or the probeswill be shorted out.

TESTINGAfter connecting the battery,

switch on, and short out theprobes with a short length ofwire. A rapid clicking, possiblyeven a buzz, should be heardfrom the loudspeaker. If there isnothing, the things to check arebattery polarity, transistor con-nections, the polarity of thecapacitor, and to make sure thatall the soldered joints are firm.

Assuming that something isheard from the speaker, grasp

40mm

100mm

details. Also shown are details of the probe.

the probes firmly in both hands. The clicking should continue, butmuch slower (body resistance is roughly the same as that of drysoil). Now insert the probes into samples of soil with varyingmoisture content. If, in general the clicking is too rapid, add somemore insulation tape. If it is too fast, remove some. If this makesno difference try changing the value of Rl. The value given should,however, be adequate.


The Extra, -ordinar

Experi-ments

ofProfessErnes

Evemureby phony John Bassett

THE Prof. has just constructeda simple contact -microphone

which can also be used to testvarious materials for piezo-elec-tric activity. By placing a slice ofmaterial which has been coatedwith metal or graphite on itsopposite sides, underneath aspring, the experimental samplescan be changed very easily.

"Here is an interesting sample,Bob," the Prof. remarked. Hecarefully unwrapped a tiny discof metallic appearance from itstissue -paper packaging. "It is aspecially prepared ceramicmaterial which has been silver -coated on its opposite faces bythe manufacturer. We'll try thisin the contact -microphone, as Ithink you'll find the result is quitesurprising."

Bob turned down the volume onthe audio amplifier whilst theProf. lifted the spring and care-fully substituted the ceramic discfor the previous sample. With thedisc firmly in place, Bob turnedthe volume back up. Immediatelya loud rustling and rumblingsound came from the loudspeaker,and a startled Bob quickly turnedthe volume back down again.

"Wow, Prof! That is amazing,"Bob cried out in astonishment."That little disc is obviously verymuch more sensitive than theother samples which yousuggested. You were still handling

the contact -microphone when Iturned up the volume and thesound was picked up and ampli-fied to such an extent, that Ithought it might damage theamplifier!

"With such high sensitivity it ishardly surprising that ceramicsare used so much in pick-ups andmicrophones!"

"Yes," agreed the Prof., "andceramic materials have a numberof other advantages, when usedfor piezo-electric purposes, overgrown crystals of materials suchas Rochelle Salt and quartz.Although the ceramics materialsare not as easy to prepare as, say,crystals of Rochelle Salt, I willdescribe their preparation brieflyto you, and then you will seewhat some of these advantagesare, and how they come aboutduring the production processes.

"In many ways the productionof these materials is similar to themaking of other ceramics such asunglazed pottery and porcelain,which are made by carefullyshaping a wet mixture of clays,drying it out, then heating it toa high temperature in a kiln.

BLENDING"When the claylike mixture is

prepared, one obvious advantageis that other ingredients can beblended in, to modify t h e

properties of the p r o d u c t.Materials can be added to makethe product stronger, to changeits density or its co -efficient ofthermal expansion, to make itsoutput more linear and to modifyits properties in many, many de-sirable ways which cannot bedone with grown crystals.

A DANGER"A disadvantage is that many

of the materials used at this point,such as lead zirconate, and bariumtitanate, are poisonous, and pre-cautions must be taken to ensurethat the material is not eaten orallowed to enter cuts or wounds,and that any airborne dust orfumes are not breathed in.

"When the material has beenblended, it can be shaped, by pres-sing, moulding or stamping, intoshapes which may be simple, likethe disc which we have here, orrings, squares, cylinders, bowlsetc, and also other more compli-cated shapes may be preparedwith electrically conductinginserts moulded in, and each ofthese shapes has special uses.

"When the shapes are fired inthe kiln they change slightly dueto shrinkage, so that whereveraccuracy is required, the finalshape and dimensions are reachedby grinding the ceramic after ithas been fired.


POLARISATION,MAGNET OR ELECTRET

"Thin coatings of silver, orother electrically -conducting sub-stances, are applied and thematerial is then polarised.""What does this mean, Prof?"Bob enquired, "Is it something todo with magnetisation?"

"The polarisation of a ceramicmaterial for piezo-electricpurposes is very similar in someways to magnetisation, Bob, butinstead of using a magnetic fieldwe use an electrostatic field.Instead of becoming magneticallypolarised like a magnet, thematerial becomes electricallypolarised. Sometimes a materialwhich has been permanently elec-trically polarised is referred to asan electret.

"The effects of temperaturechanges are very important duringthe process of polarisation. If weconsider the classic case of acharged capacitor with a soliddielectric, and use the conceptof lines of force to represent theelectric field, the capacitor canbe represented by a simplediagram." The Prof. drew a sketch(Fig. la.)

"Now if we remove the con-ductive plates from the dielec-tric", the Prof. again sketched onhis notepad (Fig. lb), "the dielec-trice remains charged. The linesof force of the electric field areheld in place in the dielectric bythe electric charges which remainon its opposite faces. But the

\ \I+ + + + +I+ + + + +

\-/ / / \

Fig. I. Lines of force associated with acharged capacitor (a) with conductiveplates (b) without plates.

dielectric is only temporarilypolarised, and by removing thecharges, which can be done byre -assembling the capacitor anddischarging it, the electric fieldcan be made to disappear." (Thiscan be done with different metalplates, proving that the chargedfield resides in the dielectric.)

ELECTROPHORUS"Prof!" Bob interrupted

excitedly, "that reminds me of areally interesting experimentwhich we did at school with agadget called an electrophorus. It

produced such a powerful electricfield that it caused small objectsto take off and hover in mid airor fly through the air. After theschool teacher showed us that,there was quite a crop of home-made ones which the lads madefor themselves, and I was sofascinated that I made one myselfat home. Next time I come to seeyou I'll bring it to show you!"

"Hmmm, yes" mused the Prof.,it's quite a while since I lastexperimented with an electro-phorus. It's also quite late, I mustremind you."

Bob in his enthusiasm hadstayed much later than he hadintended, and as he looked withdismay at the time displayed inhuge luminous figures on theviewscreen of one of the Prof'scomputers, and hastily preparedto leave, the Prof. continued: "I'llbe interested to see your home-made electrophorus so I hopeyou'll bring it soon! It willcertainly help to illustrate anddemonstrate some of the pointsI am explaining about polarisa-tion, and then we can continueour discussion of piezo-electric,magnetic and various types ofpick-ups. See you soon, Bob."

"Yes, bye Prof," and Bob hastilymade his way out of the labora-tory and sped off home, his headfull of thoughts about electricpolarisation pick-ups and micro-phones and anticipation of hisnext visit to show the Prof. hishome-made electrophorus.

To be continued

Readers' Bright Ideas; any idea that is publishedwill be awarded payment according to its merit. Theideas have not been proved by us.

HEAT SHUNTI have thought of a tip that may prove useful to

constructors. It is the use of a split pin as a heatshunt for use on transistor and diode lead -outswhen the latter are being soldered in place.

I have been using a 4mm thick pin with the

ends of its legs cut square, one being longer thanthe other. The pin then clips over the lead -out onthe component side of the board and is smallenough to thread its way in among other com-ponents in the vicinity.

0. Maxwell,I.O.M.

P.C.B. AIDI have recently come across a way of accurately

placing an integrated circuit on a piece of copperclad printed circuit board.

Take a small piece of 0 I inch matrix strip -board and drill through the holes where the i.c.pins go through using a No. 45 drill (2mm).

This then acts as a template, for it can now beplaced in the required position on the copperside of the p.c.b. and a sharp pointed pencil usedto mark each hole through onto the board. Theoutlines produced are next filled in using an etchresist pen, and the rest of the pattern then drawnon in the usual way.

I have found this ideal for making printedcircuit boards using i.c.s of various kinds.

K. Nuttall,Bureley,

Lancs.


Quasi -Quad QueriesI am one of your so called non-

specialist onlookers, and whilst brows-ing through your March '77 issue, I

decided that I would have a go atconstructing the Quasi -Quad Adaptor.Being a potential starter, with yourarticle my trainer, I am writing to ask afew questions and ask for tips.

I have had limited experience ofelectronics ('A' -level Physics failure,and I have knocked up radio's etc. fromkit form and many years ago playedwith those early Phillips kits of electricwizardry for the under -15's), but I havenever touched a circuit -board and I wasconfused by the diagram of Fig. 5 (page116), of the Quasi -Quad Adaptor article,

as I cannot differentiate between the"dots" and "circles" etc. Could youclarify?

Another point I do not understand(or cannot visualise) is the fitting ofcopper strips to act as heatsinks to thewhole of the stripboard (or is thisbecause I have never seen a section ofstripboard?).

Also the LM380 has a rated output of2 watts, but in my stereo system (20watts per channel), this would surelynot suffice, as on average, the outputwill be at 8 to 10 watts per channel.Does this mean that the speakers willbe at less power, i.e. less volume? Willthis destroy the effect created (es-pecially if four similar speakers areused)? And lastly is there any realdanger to my hi fi system if I make aconstructional error?

J. Westray,London SE23

The area of Fig. 5 you refer to (dots andcircles) shows the underside of a piece ofStripboard. Stripboard consists of stripsof copper (shown white) bonded to asynthetic board (shown black). The boardis perforated, with holes drilled on aregular matrix at 0.1 inch or 0.15 inchpitch. Not all these holes are shown onthe drawing in order to avoid a clutteredeffect, in fact only those immediatelyinside the perimeter of the board areshown.

The black dots you refer to are thesoldered connections of the componentleads (sited on the topside of the board-shown adjacent to the underside view) tothe copper strips. What at first sightappears to be a white dot surrounded by ablack area is used to represent a breakalong the copper strip made by using saya twist drill.

286

The second part of your query should beanswered by the above and by youinspecting a piece of stripboard.

Concerning the power rating of theLM380, this should be adequate. You areover -estimating the listening level. Forcomfortable listening in the home, youramplifier will only be delivering about I

watt or even less.See Please Take Note in April issue

for wiring correction.

Indentification DataService

With respect to Mr. Pascoe's pleafor someone to operate a device dataand identification service I am willingto undertake this operation for a costof 10p per device for a minimum of 10devices. An additional 15p needs to beincluded for postage and packingexpenses. With respect to i.c.s itwould be helpful if one or two of themcould be sent to assist with theiridentification.

R. Houghton,49 Addington Road,

Irthlingborough,Northants.

Lin. and Log.I am aged 12 and have been reading

your magazine for quite a while now. Ihave constructed some of your "starterprojects" and am now ready to con-struct the Transistor Tester in the May '74issue. (I found it while looking throughsome of my back -copies.)

One thing that puzzles me is linear,logarithmic, anti -logarithmic etc., whenreferring to potentiometer slider ro-tation. I would be grateful if you couldexplain these to me. Keep up the goodwork publishing an excellent magazine.

Paul Bailey,Rutherglen, Glasgow

The terms, logarithmic (log.), linear(lin.) and anti -logarithmic (anti -log.)refer to the variation of resistance betweenthe slider and one end of the potentiometeras the shaft is rotated. In a linear type, theresistance is directly proportional to theangle of rotation, i.e. if 45 degreesrotation produces 10 kilohms, then 90degrees rotation produces 20 kilohms.

Now in a log. type, the variation ofresistance with angle of shaft rotation,obeys a logarithmic relationship i.e. if a45 degree rotation produces 10 kilohms,then 90 degrees rotation produces 100kilohms. A further 45 degree step in-creases the resistance to 1,000 kilohms(I megohm).

The anti -log. type potentiometer, hasas its name implies an anti -log relation-ship of resistance with shaft rotation.

Revival RallyWe have been informed by the Radio

Society of Great Britain, that a rally,named the "East Suffolk WirelessRevival" is to take place at the CivilService Sports Ground, Straight Road,Bucklesham, Ipswich The rally will beopen from I lam to 4pm, 29th May 1977.

It is intended to revive some of theinterest and enjoyment of the "pre -black box" type of rally The emphasiswill be on finding out, participating aswell as purchasing.

By holding the event out of doorsrather than in a school or hall, whilstproviding covered areas for tradersand demonstrators, there will befreedom to move around with thefamily or just sit and ragchew.

Trade participation and the abilityto look for that special component etcwill be well catered for in a largemarquee. Presenting practical demon-strations, competitions and informationit is hoped to encourage attendancefrom licence holders, short wavelisteners (swl) and those interested inthe whole spectrum of amateur radio

It is hoped that by reference to thosewith experience, ideas as to solutionswith problems on T V and radiointerference etc may be found.

A comprehensive range of equipmentwill be used to provide a facility fortesting mobile equipment and anantenna test range to check the gainof both professional or home builtaerials brought to the rally It is hopedto arrange demonstrations, to bothencourage the newcomer and interestthe active participant in, RTTY,RAYNET, SSTV etc.

Plastic MoneyI have read with interest the Counter

Intelligence article in the March '77issue of E.E. and note the commentsregarding the "Metal Strip" in poundnotes This metal is in fact a fine stripof polythene which has been sand-wiched between two pieces of finequality paper.

I note that the editor makes mentionin his editorial of the "barrier" whichoften surrounds the whole subject ofelectronics. I have to date assembled acapacitive discharge electronic ignitionsystem kit and the Wiper Delay unitpublished earlier this year in E.E.Other than this the subject is very newto me.

The greatest hurdle is understandingyour abbreviations and nomenclaturesof components, i.e. s.p.s.t.; 500 kilohmcarbon lin.

Is it practical to publish some form ofdictionary or supplement to helpbeginners like myself to understandwhat these abbreviations mean? Apartfrom this I find E.E. easy to follow andmost interesting.

J. Little,Yorks.

We have recently, in the Feb. and Aprilissues published a list of abbreviations oftechnical terms used in E.E. It is hoped topublish such a list from time to time andpossibly extend it to include such thingsas explanations of . . . 500 kilohm carbonlin. The latter refers to a potentiometerwhose maximum resistance is five -hundred -thousand ohms, is constructed(internally) of carbon and has a linearresistance/rotation relationship. See replyto Mr. Bailey's letter above.


LAST month, details of the mixer,oscillator, and i.f. amplifier

were given. We continue thismonth with the construction anddetails of the optional b.f.o. unit.

Note once again that Dencocoils should now be used, as men-tioned in part one (May '77 issue).

PANEL AND CHASSISThe case sides are plywood,

190 X 115mm, and the chassis a255 X 100mm "universal chassis"flanged member secured withfour bolts through the flangeholes, and set 63mm back as inFig. 5. The chassis top is at aheight of 38mm.

The panel is a similar member,but is fixed vertically with boltsthrough the flange holes, andleaving about 35mm clear be-tween chassis and panel, as inFig. 5. Holes for the lower con-trols are 25mm from the bottom,and 41mm and 100mm from thesides. Variable capacitor VC2 ismounted as shown in Fig. 5, sothat the drive drum is about 3mmclear of the panel top.

A piece of wood 127 X 45 X10mm thick is screwed to thepanel to carry the scale.

Pivot one of the drive pulleyson a bolt as shown in Fig. 5 sothat the top of the cord is level;the second pulley is mountedabout level with the bottom ofthe drum. The cord has one com-plete turn round the tuning con-trol shaft, and runs over thepulleys to the drum. Here, theends are taken through the peri-meter slot, and are tied to thespring, which keeps the cord taut.

A scale about 100mm long isneeded, and in the author's modela lOcm paper rule was used,glued to card which was in turnstuck to the wood. A small pieceof tinplate is bent and clipped tothe cord with pliers, and thepointer is a straight wire solderedto this.

The front of the receiver isPerspex, 250 X 100mm, coveredwith self-adhesive material inwhich an aperture 115 X 28mm iscut, to match the scale position.Thin plywood or a metal frontcould be used instead, with an

aperture cut in it. The front issecured by four 613A bolts (atleast 25mm long) w ith extra nuts,and running through the holespresent in the flanged member.

ADDITIONAL WIRINGThe boards are filled as shown

in Fig. 5, which also shows inter-connecting wiring. Inductors L.5and L6 are secured with 6BAbolts, and wired to a tag (MC)bolted to the chassis. After mak-ing the connections of Fig. 5,reference should be made to Fig.6, an underside plan with thepanel shown flat to clarify theswitch wiring. It may he pre-ferred to first wire S1/4 for onewaveband only and then test thetuner. If this system is not used,take special care to ensure thatthe correct tags are used in wir-ing up the switch.

Inductors LI and L2 arewound on a cored former llmm(716 inch) in diameter, althoughformers of 9mm to 13mm (38 to 12inch) diameter would be suitable.

Designed to receive transmission on short, mediumand long wavebands,

Neeite--gsaadNER

PART 2

287

L3 ),, L4mirnm..3,3,..., ,,,,r, r

01111111 'I.MC Of ''...."..

T1 (1)'

BOARD B

u n

DI/c19 CHASSIS

R12

RSA .1121(d)

SK3

R5.,,C4

MC

BOARD A

8 -.

2 4L5

3 1

- L6

RED RED

mc

B1 -Kve

C 5 R14/C3

....--11.S41S) S3IS) S4(MIL) 53114.1

A S6S3(POLE)

VC2 PAMAMR R1

DRUM WOOD CORD SCALE1 POINTER40mm --4,- 29mm--.-

Fig. 5. Topside view showing position of component boards. Note that Wearite coils are shown asused in the prototype.

The secondary winding of L2(points 1 to 2, Figs. 1 and 6) con-sists of 31 turns of 26 s.w.g.enamelled copper wire, the turnsbeing wound side by side. Theprimary winding of Ll (points 3to 4) is made up of 8 turns ofcotton -covered wire (or enamelledwire on insulating tape) of 26 to32 s.w.g. The ends of 2 and 4should be taken to the tag MC, towhich also is wired the stator con-nection of VC1. Ends 1 and 3should be long enough to reachSi and the aerial socket. A fewtouches of adhesive should beused to secure the coil turns inplace.

A 75 x 25mm strip of wood orpaxolin is bolted to the rearflange of the chassis (Fig. 5) andthe ferrite rod is secured to thiswith adhesive and thread orstring. Coils L3 and IA are posi-tioned as shown and the leadoutwires are taken to a small tagstrip near the rod, so that longerleads can be run to S1 and S2;IA must be the correct way round

on the rod, as shown in themaker's leaflet, otherwise it willnot be possible to obtain properlong wave tuning.

DIAL MARKINGSA slow-motion drive is not

essential for the aerial tuningcapacitor VC1, but it should beprovided with a pointer. The twomultiway switches will also re-quire pointers. The scale for S1/4should be marked up as follows:Mark the L position: 125-309kHzMark the M position: 500-1685kHzMark the S position: 10-2.9MHz.

The scale for S5 should bemarked up as follows:

On the L band, mark position 6309-238, position 7 238-191, posi-tion 8 191-158, position 9 158-125.

On the M band, mark position1 1685-885, position 2 885-620,position 3 620-500.

On the S band, mark position 110-7.3, position 2 7.35.7, posi-tion 3 5 -7-5 0, position 4 5.04.4,position 5 4.4-3-9, position 6 3.9-

3.6, position 7 3.6-3.35, position8 3.35-3.2, position 9 3.2-2.9.

The bands are arranged so asto discount the slight overlapwhich will be found at the ex-treme positions of VC2 rotation.

The use of three differentcolours will make the scale of S5easier to read. See Fig. 9 forsuggested arrangement of themarkings for the two wavebandswitch scales.

TUNINGSet the switches for the fre-

quency sector required. Thentune in signals by means of VC2and peak them with rotation ofVC1. The handling of the two con-trols will soon become simple inpractice. If VC1 cannot reach thelowest frequency on band S whenfully closed, screw the core of L2slightly into the winding. Simi-larly, place L3 and L4 on theferrite rod so that VC1 covers thewanted ranges with a little tospare.


SK1(AERIA

S7

VC1

56

Cl

Fig. 9. Suggested markings for thetwo waveband switches. These aredrawn full size, and may be traced.

MC

C20 C22R13

If® ®

C21

PANEL

OIrLIVE1

CHASSISMC

Fig. 6. Wiring details of the two waveband switcnes.Note that the front panel has been opened out flat for

clarity.

1F

(SEE,TEXT)

Fig. 8. The b.f.o. unit is wired on a small tagstrip asshown here. MC denotes a direct connection to themetal chassis. Usually made by fitting a solder tag with

a nut and bolt.

e c b

TR5 VIEWED FROMUNDERSIDE

/co

5

3636

"ra

')or

1685 kHz

I

.1\ ?s,

`;'0

4.4 -,---

c3,s,

3.g

309

A,

I I I

0, ? % ct"

\ /\ St,/' ca

ez 6 9

8


,,11..M11

The aerial for short wave recep-tion may be an outdoor one ora wire indoors (perhaps runningalong a picture rail or similarly,as high and long as practicable).

If an earth is available, thisshould be plugged into a socketconnected to MC. A short aerialwill provide reasonable results onthe more powerful stations, butfor the weaker signals a long out-door wire will give considerablyimproved results.

BEAT FREQUENCYOSCILLATOR

This unit is required only if theoperator wants to receive c.w.and s.s.b. signals satisfactorily.Amateur and commercial stationsusing Morse code do so by usingc.w. transmission (an interruptedunmodulated carrier wave) whichnormally cannot be heard on anordinary receiver. Some stationsuse m.c.w., which is a c.w. signalmodulated with an audio tone sothat it can be heard on anyreceiver

The function of the b.f.o. is torender the c.w. signal easilyaudible. It is basically a simpleoscillator and when in use theb.f.o. signal beats with the incom-ing c.w. signal to produce aheterodyne signal at a predeter-mined audio pitch.

With single sideband signals,the carrier wave and one side -band have been removed. Thecarrier/b.f.o. unit supplies a car-rier at the tuner, thus enablingthe s.s.b. signals to be resolved asspeech This form of transmissionis widely used by amateurs, par-ticularly in the 3.5-3.8MHz band.

The circuit of the carrier/b.f.o.unit is shown in Fig. 7. The b.f.o.coil L7 is a Red Range 2 valvetype coil and it has C21 in parallelacross its primary winding to com-plete the tuned circuit. Adjust-ment of the coil core allows theoscillator to be tuned to the cor-rect frequency, after which thecore should be locked with a6BA nut.

Switch S7 is the on/off switchwhich puts the b.f.o. off for a.m.reception. The purpose of thelarge value C23 is to preventmodulation of the oscillator viathe battery supply.

The coil L7 is supplied in a canwhich serves as a screen. The lidshould be bolted on the chassisbehind the volume control, and

IF

R13

330ka

121C050pF

BLACK

WHITE.

RED

I "T

BFOCOIL

I.

ORANGE

TR52N3704

C8021

057

ON/OFFRI46.842

T0 -

C22 C2305pF 100pF

ov

9V+

Fig. 7. Circuit for the b.f.o. unit used in the Multi -band tuner.

a 6mm hole for the leads shouldbe provided. Next drill the bottomof the can to take the coil. Solderon four leads (which may becolour coded) to the pins shownand take the leads through thehole and out under the chassis.

The other components aremounted on a tag strip as shownin Fig. 8, the oscillator coil L7fitting nearby on the case side. Alead should be run from the tagused as a junction for the leadfrom coil lead 8 and along underthe chassis and up to the pin from

T1 (pin 1) on the i.f. board; thislead should be looped round thepin without removing the insula-tion. Because injection is at thei.f. amplifier input, this very smallcoupling capacitance is sufficientfor the purpose required.

B.F.O. ADJUSTMENTThe b.f.o. performs best with

the audio gain at or near maxi-mum; if necessary the volumecan be kept down by slightly de -tuning VC1. First tune in any

Underside photograph, showing the waveband switches, and the b.f.o. unit.


stable broadcast with the b.f.o.switched off. Then switch on (S7)and rotate the oscillator coil coreuntil a strong heterodyne is ob-tained. This will fall in pitch asthe correct core position isreached and rise again as it ispassed. Set the core at the posi-tion where the tone is very lowin pitch, or ceases. Slight detun-ing by means of VC2 either waywill then produce an audio tonewhich rises as the tuning ismoved away from the correctposition.

Next, find a weak s.s.b. signal,which will be recognised as dis-torted, chopped up speech (trythe 3.5-3.9MHz amateur band)and tune it for maximum volumewith S7 switched off. Then switchS7 on and very slightly adjustthe core of the b.f.o. coil, if neces-sary, for proper resolution of thespeech. The core should then belocked in position.

With a.m, signals, of course,tuning should be made for thebest volume. With c.w., note thetuning will change the audiopitch. With s.s.b., tuning is more

Photograph showing the completed prototype tuner.

critical for proper reception butis aided by the bandspreadingeffect of VC2.

It should be remembered thata supherhet tuner can providereception of signals on its "secondchannel". This image appears930kHz higher in frequency than

the proper, wanted, signal on thistuner but is only likely to causeproblems on the higher frequen-cies and with VC1 tuned to placethe aerial circuit on a higherfrequency than the oscillatortuning.

GREENWELD443 N/lillbrook Road SouthamptonSO1 OHX Tel:(0703) 772501

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Megohm, total 610 for £6 00. Save£3.15!Electrolytics, 10 each value 1, 2.2,4.7, 10, 22, 47, 100uF, All 25V. Total70 for £3.20. Save 41.101CAPACITORSMiniature ceramic plate from 22pF to1000pF 5% 2p; 1500pF to .047 4p.Mylar 1000pF to 8200pF 5p each.Polyester -01 to 0.1 uF 4p; .15, .225p;-33 5p; 47 8p; 038 10p; luF 12p; 2-216p.Electrolytic, 25V working: 1, 2'2, 4.7,10, 22, 47uF All lip; 100uF 7p; 220uF9p; 470uF 16V Op; 470uF 25V 11p;470uF 63V 18p ; 1000uF 16V 15p;1000uF 25V lop; 1000uF 50V 32p;1000uF 63V 40p; 2200uF 16V 20p;2200uF 25V 29p; 2200uF 40V 4$p;4700uF 16V 43p; 4700uF 25V Sip;All the above are wire ended. Tagended 4700uF 40V 72p.

SOLDERLESS BREADBOARD I NG-DECSThe famous DEC System of Solderless Breadboarding is ideal for both the youngand more mature students of Electronic Engineering as it enables circuits to betried and tested without the use of soldering and because of the specially de-signed contacts allows components to be used over and over again. It is alsoextremely useful for the Circuit Designer who wishes to experiment with andperfect his circuit quickly yet economically.

S -DEC (Model PB11)This, the most popular Board, is designed solely for the use ofdiscrete components and is particularly useful for basiceducational purposes.(No. of Contacts: 70) 1 off £1.98

5 off £1 76

T -DEC (Model PB21)This Board allows 2 TO5 or 1 DIL IC Station to be used and sois primarily intended for discrete work or for linear IC applica-tion where considerable numbers of discrete components maybe required.(No. of Contacts: 208) 1 off £3.62

5 off £3 21

ii -DEC 'A' (Model PB31)The M -DEC 'A' is specially designed for ease of use with IC'sand allows 2 DIL or 4 T05 stations to be used but will accom-modate discrete components with equal facility.(No. of Contacts: 208) 1 off 1E3.97

5 off £3 53

p. -DEC 'B' (Model PB41)The µ-DEC 'B' is for similar uses as m -DEC 'A', but has two16 lead IC sockets as part Of the Board.(No. of Contacts: 208) 1 off £6.97

5 off E6 19

DEC ACCESSORIES16 DIL adaptor (with socket) P806210 TO5 adaptor (with socket) P9072Single ended leads (set of ten) P8101Double ended leads (set of ten) P0102lmm plugs (set of ten) PB103

All prices include 8% VAT. P. & P. 258.Our retail counter Is now open, stocking a large variety of audio and electronic

parts and accessories, branded and surplus

£1 92£1.80£0.90£0 99£0.45

WE ARE SITUATED 2 MIN. WATFORD JUNCTION STATION

THE COMPONENTS CENTRE7 Langley Road, Watford, Herts., WD1 3PS.

Tel.: Watford 45335


GEORGE HYLTONbrings it

own

Using Old MetersAREADER from Kent. Mr. L. N. Buik,

writes t y that he has pickedup a couple o ten Cheaply. He asksif they can b for use as testmeters.

This is a co ough situation.There are al ndhand metersaround. So let it.

The first t do (preferablybefore buying e sure a meteris operation a smoothlyincreasing cur .plied does theneedle move ? A lot of oldmeters stick '.int. Secondly,do the scale tell the truth?If the scale re. IV is the meterreally a voltm st an ordinarymoving coil ga r masqueradingas one?

Pocket UniA simple t (Fig. I) answers

both question ntend to go ona meter hunt local shops it'sa good idea t this circuit asa pocket size o test a meterconnect to t A" range andturn up VR deflection isproduced leave VRI' at the halfwaypoint and sw tch 52 to progressivelyhigher current rangps until somedeflection appears, however small.Then adjust VRI sl 'ly to vary thedeflection up to ful tale and backagain, watching for ing points.

If all appears well, a range whichgives a substantial de ction with VRI

toeart292

at maximum. In this position thecurrents on Fig. I are approximatelycorrect. So you can see if the calibrationof the meter is about right.

If the meter is a voltmeter thedeflection will be about the same onall the higher current ranges. But manymeters marked in volts are reallycurrent meters designed to be con-verted into voltmeters by adding anexternal series resistance (called amultiplier).

VoltmeterOn the whole the most useful

meters are voltmeters but a reasonablysensitive current meter (1mA fullscale or less) can easily be convertedinto a voltmeter. I'll illustrate how it'sdone using one of our reader's metersas an example. This is a 750µA"galvanometer" (moving coil d.c.meter) scaled 0 to 100. Its dial carriesthe useful information: Resistance14 ohms @ 20°C.

resistors the error due to the tolerancecan be far greater than 14 ohms. In anycase the full scale current may not beexactly 750µA so unless you can checkthis against an accurate meter you justdon't know whether it's worth buyingclose tolerance resistors. I suggestcheap 5 per cent ones: most voltagemeasurements in electronics don'tneed to be made with great accuracyanyway.

Other voltage ranges can be obtainedby using a different multiplier calcu-lated in the same way. Thus for a 300Vrange the total resistance is 300V/750µA =400 k 'ohms.

Higher Reading AmmeterOur reader's other bargain meter

was 15mA d.c., resistance not given.This is too insensitive for use as avoltmeter but is quite handy as itstands since currents in the 0 to 15mArange are frequent in transistorcircuits. If a higher range is requiredand you can find out the resistance

Si

82k1) (110pA)

27k1)(330pA)

8.2k12 (1-1mA)S2

VR12.71(0(3.3mA)

mloI

IB1

9V 82012(10m A)

4-7k11OR 10k12VOLUMECONTROL METERWITH SWITCH IS11 UNDER

27012 (33mA) TEST

Fig. I. The circuit diagram of the pocket meter tester. This may be constructed ina small plastic box, with VRI/S1 and S2 on the front panel. Two leads terminatedin crocodile clips are used to connect the meter under test to the unit.

Ohm's LawTo use a "0 to 100" scale the voltage

range must bear some simple relationto 100. Let's make it IV. Then with10V applied the current has to be fullscale, i.e. 750µA.

By Ohm's law the resistance mustthen be I OV/750µA=13,333 ohms. Themeter itself provides 14 ohms so themultiplier must provide the rest; i.e.13,319 ohms. This is not a standardvalue. A fairly close approximation isgiven by 15 kilohm in parallel with120 kilohm, both standard E I 2 seriesresistances. These give 13,333 ohmswhich as we've seen is too high by themeter's own resi'stance. But in practiceIS kilohm and 120 kilohm are as goodas you'll get without great expense.Even if you buy I per cent tolerance

(please don't try to measure it on anohmeter or you'll wreck your bargain)it is possible to connect a "currentshunt" resistance across the meterterminals.

For example suppose the 15mA meterhas a resistance of 9 ohms and you wantto make it read 0 to 150mA. At fullscale 15mA must go through the meterand the other I35mA through theshunt. Since the voltage drop acrosstwo resistances in parallel is the samefor each of them and since 135 is ninetimes 15 it follows that the shunt mustbe one -ninth of the resistance of themeter; i.e. I ohm in our example.

Unfortunately real -life meter resist-ances seldom work out quite as easilyas this one and making shunts is a lotless simple than making voltagemultipliers.


Bring tcope/to your interest.There's only one way

1 Build an oscilloscope.As the first stage of your training, you

actually build your own Cathode rayoscilloscope! This is no toy, but a testinstrument that you will need not onlyfor the course's practical experiments, butalso later if you decide to develop yourknowledge and enter the profes'sion. Itremains your property and represents avery large saving over buying a similarpiece of essential equipment.

to master electronics...to see what is goingon and learn by doing.

This new style course will enable anyone tohave a real understanding of electronics by amodern, practical and visual method. Noprevious knowledge is required, no maths, andan absolute minimum of theory.

You learn the practical way in easy stepsmastering all the essentials of your hobby or tofurther your career in electronics or as a self-employed electronics engineer.

All the training can be carried out in thecomfort of your own home and at your ownpace. A tutor is available to whom you canwrite, at any time, for advice or help duringyour work. A Certificate is given at the end ofevery course.

T

Read,draw andunderstand circuitdiagrams.In a short time you will be able to

read and draw circuit diagrams, under-stand the very fundamentals of television,radio, computors and countless otherelectronic devices and their servicingprocedures.

All students enrolling in ourcourses receive a free circuitboard originating from aComputer and containingmany different componentsthat can be used in experiments and provide an

,electronic practice.excellent example of current !ADDRESS

C D

4 5 6 ?r-gEgAlk

3Carry out over 40experiments on basiccircuits.We show you how to conduct

experiments on a wide variety of differentcircuits and turn the information gainedinto a working knowledge of testing,servicing and maintaining all types ofelectronic equipment, radio, t.v. etc.

To find out more about how to learn electronics in a new exciting and absorbingway,just clip the coupon for a free colour brochure and full detailaof enrolment.

'Write to:- British National Radio & Electronics School, IP.O. Box 156, Jersey, Channel Islands.

NAME

1.=EEB 67


RECEIVERS and COMPONENTS

Three assorted meters 12111. T.V. convergencePanel. ExAC128. 3 slugged coils, 3 slide switches11 W.W. Pots, 3 Carbon Presets, 2 Ferrite Chokesetc. 11,10. Small audio amp. 3 Transistors,Equiv. AC128.0072 with circuit 40p, 3 for Et.Talking Paps Panel 12 silicon Transistors, SCR,2 pots etc. Et. 100 assorted C280 polyester caps£1 15. 71b. assorted components 42 75.List 15g, refund on purchases. Over 41 post paid,under add 20p. Insurance add 10p.

J. W. B. RADIO,2, Sarnfleld Crescent, Sal*, Cheshire M33 I NL

NO LICENCE EXAMS NEEDEDTo operate this miniature, solid-state TransmitterOnly £8.25 plus 20p P&P.'Brain -Freeze' em with a MINI -STROBE Kit, pocket -sized 'lightningflashes', varl-speed, for discos andparties. A mere £3.80 plus 20p P&P.Experiment with a psychedelicDREAM LAB, or pick up faintspeech/sounds with the BIG EARsound -catcher; ready-made multi-function modules. £5.00 each plus20p P&P.LOTS MORE! Send 20p for lists.Prices include VAT. (Mail orderU.K. only).

BOFFIN PROJECTS4 Cunliffe Road, Stoneleigh

Ewell, Surrey. (E.E.)

SMALL ADSThe prepaid rate for classified advertisements is 14pence per word (minimum 12 words), box number40p extra. Semi -display setting f9.00 per singlecolumn inch (2.5cm). All cheques, postal orders, etc.,to be made payable to Everyday Electronics andcrossed "Lloyds Bank Ltd." Treasury notes shouldalways be sent registered post. Advertisements,together with remittance, should be sent to theClassified Advertisement Manager, Everyday Elec-tronics, Room 2337, IPC Magazines Limited, King'sReach Tower, Stamford St., London, SE1 9LS.(Telephone 01-261 5918).

CONDITIONS OF ACCEPTANCE

OF CLASSIFIED ADVERTISEMENTS

1. Advertisements are accepted subjectto ths conditions 'pouring on our currentadvatisiment rats card end on ths amassunderitamilng that the Advertiserwarrants that the advertisement dots notcontravene any Act of Panamint nor is itan Infringement of the British Code ofAdvsnising Practice.2. Tha publishers risme the right torefuse or withdraw tiny advatisamint.3. Although every cars is taken, thsPubilihors shell not be liable for clericalor printers' errors or their consequences.

DISCOVER ELECTRONICS, Buildtwenty easy projects including: MetalDetector; VV ireless Transmitter;Breathalyser; Miniature Radios; Stetho-scope; Lie Detector; Touch, timeswitches; Burglar Alarms, etc. Circuits,plans all for £1.29 including circuitboard. Mail only. Ridley photo/elec-tronics, Box 62, 111 Rockspark Road,Uckfleld, Sussex.ELECTRONIC DICE as March EE.Complete kit -send £3.66. Case extra58p. Components catalogue 25p (re-fundable). MAGENTA ELECTRONICSLIMITED, EEB, 61 Newton Leys,.Burton on Trent, Staffs DE15 ODW.

FOR SALE

COMPLETE SET. E.E. Issue 1 topresent. Offers. BIGGS, 25 Gay ElmsRoad, Withywood, Bristol.BACK NOs, available of E.E./P.E./P.W.Miscellaneous copies from 1967 to1975. Also some complete volumeissues. Offers, enquiries SAE please,to E. SHAW, 67 Wellstone Garth,Bramley, Leeds 13, Yorks L'S13 4EJ.FIRST 28 Everyday Electronics plusDemo Deck £25. Buyer collects. Ched-dington 668193.

BOOKS and PUBLICATIONSSIMPLIFIED TWIREPAIRS. Full repairinstructions individual British sets£4.50, request free circuit diagram.Stamp brings details unique TV pub-lications. Ausee, 76 Church Street,Larkhall, Lanarkshire.BUILD 5 TRIED AND TESTED CIR-CUITS. Digital Precision Timer (2

30min). Sensitive burglar alarm. Volt-meter/Ammeter. A. F. Circuit tracer.Metal Detector. Diagrams 50p each+SAE (£2 for 5). Buildit, 100 Coltstead,New Ash Green, Kent DA3 8LW.

WANTEDWANTED. Info on Govt. SurplusMonitor Unit Type 56. 41 Ronald Road,Liverpool L22 3XU.

SERVICE SHEETS

BELL'S TELEVISION SERVICE forservice sheets of Radio, TV etc. 75pplus SAE. Colour TV Service Manualson request. SAE with enquiries toBTS, 190 King's Road, Harrogate,N. Yorkshire. Tel: 0423 55885.

SERVICE SHEETS, Radio, TV, etc.,50p and SAE. Catalogue 20p and SAE.Hamilton Radio, 47 Bohemia Road, St.Leonards, Sussex.

MISCELLANEOUS

STYLI, CARTRIDGES & AUDIOLEADS ETC. For the best at keenestprices send SAE for free illustratedlist to: FELSTEAD ELECTRONICS,(EE), Longley Lane, Gatley, Cheadle,Cheshire SK8 4EE.

BARGAIN BOX for BEGINNERS containing2 Transistor/component panel., 1 Relay, 1

Rectifier, 1earphone Insert, 1 mike insert, 2 diodes,1 buzzer, 3 core cord, 1 salvaged tool -an Idealcollection for experiments: E1110 Inc. VAT &P.P. 5 digit counter. 10 digits/sec., 24-48v. non -reset, brand new GPO type II5p inc. Also 3, 4, 6,6 & 9 core cords many other telephone spares atgive away prices!Trade enquiries welcome. S.A.E. for lists ororders to:

B. B. SUPPLIES141, Shalmsford St., Near

Canterbury, Kent. CT4 7QZ.

THE 0 - EN DOOR TO QUALITYTHE COVERIS BLACK& WHITE

4th ISSUE INCLUDES NEW METERSThis 144 page catalogue-Electrovalue Catalogue No. 8 (Issue 4, up -dated)offers items from advanced opto-electronic components to humble (butessential) washers. Many things listed are very difficult to obtain elsewhere.The Company's own computer is programmed to expedite delivery andnfaintain customer satisfaction. Attractive discounts continue on manypurchases; Access and Barclaycard orders are accepted. FREE POSTAGEon all C.W.O. mad orders in U.K. over £2.00 list value (excluding V.A.T.) Ifunder add 15t, handling charge.

BUILD WITH THE EVERYDAY ELECTRONICS

TEACH -IN KIT nett £15.75 inc. V.A.T.tocclit0 MAIE.

Cate o9ELECTRO ALOE LTD

from Electrovalue as described in this journalAll comicion. to Dept. EE4.28 ST. 3UDESRD., ENGLEFIELD GREEN, COHAN, SURREYTWPO ORB. Phone Etrham 3603. Telex 284475.NORTHERN BRANCH: 880 Homage Lane, Emmaus, Manchester5119 1NA. Phone (061.) 432 4945.Sho hours both athlreect 0-x.:30 , I p1.1 `4.,t.

144 Page

40pinc. refund

voucher worth40p


TRANSFORMER BARGAIN. 30V, 1'2Aoutput, 200 to 250V input. £2.95. Postand Package 90p VAT 8'2%. MJE 3055Transistor 48p P&P 20p VAT 12'2 %.EDENCONIBE LTD., PO Box 276, 67Gloucester Street, London SW1V 4DZ.

100 RESISTORS 75p1W 5% c/FILM 2.20-2.2M a (E12)

10 each of any valueCM CASSETTES 30p All Cassettes in PlasticC90 CASSETTES 45p Case with index and

Screwed Assembly.All prices Include VAT. Add Postage 10p In £1.Quantity Discounts SALOP ELECTRONICS,10 Units 5% 23 WYLE COP,50 Units 7% SHREWSBURY

100 Units 10% Tel. 53206

RECHARGEABLE NICAD BATTERIES`AA' (11P7)-£1.26. Sub 'G'-£1.29. 'C'(HP11)-£2.38. 'D' (HP2)-£2.92. PP3-£4.98. Matching chargers, respectively,£4.48, £4.48, £5.24, £5.24, £3.98. Allprices include VAT add 10% Post &Package. SAE for full list, 1 plus, Ifwanted, 50p for 'Nickel CadmiumPower' Booklet. Sandwell Plant Ltd.,1 Denholm Road, Sutton Coldfield,West Midlands B73 6PP. Tel. 021-3549764.

ENAMELLED COPPER WIREswg 1 lb Box 4or Sox14-19 2.40 1.20 611 -114

20-29 2 46 1 11111 112 5930-34 2 69 1.70 69 0435-40 2 -IS 1N 1-04 75

Inclusive of pap and VAT.SAE brings Catalogue of copper and resistancewires In all coverings.

THE SCIENTIFIC WIRE COMPANYPO Box 30, London E4 WSW

Reg: office 22, ConIngsby Gardens.

-.0 -fp TREASURE TRACER

MK III Metal locator Varicap tuning Britain's best selling metal

locator kit; 4,000 sold Weighs only 22oz. Fitted with

Faraday shield Speaker and earphone operation Knocks down to only 17in Prebuilt search coil assembly Thoroughly professional finish As seen on BBC1 and BBC2 TV You only need soldering iron.

screwdriver, pliers and snips Five transistor circuit

Send stamped add r dnvlooe for leaflet

Coomiole 114.75 tr ,,1,1£19.75Post ft 00 -fl 78 VA El 00 ft 53 VAT 10%)

MINIKITS ELECTRONICSBb CLEVELAND ROAD,

LONDON, £10 2AN (Mail order only)

A UNIQUEOPPORTUNITY

We can show you how to earn a lot ofmoney working part or full time from home.We are the ONLY company in the U.K. offer-ing this unique information. A basic interestin electrical engineering is necessary.Government Departments are making useof our system, why don't you. For completereturn of post details send a large stampedaddressed envelope to: -

MAGNUMDept. E.E., Brinksway Trading Estate,

Brinksway, Stockport.

GLASS FIBRE P.C.B'S.From your own tape, film or Ink masters. Sends.a.e. for quotation.Everyday Electonics P.C.B'S In glass fibre, tinnedand drilled. Dec. 76 Mini Organ £2.48. C.W.O.please. Practical Electronics P.C.B'S.Send S.A.E. for list. R. 5. Components. All of thesewell known suppliers components available.

PROTO DESIGN, 4, HIghellIfir Way,Wickford, Essex, 8811 ILA.

4 -STATION INTERCOM

+£1895V.A.I 52

Solve your communleation problems with this

4 -Station Transistor Intercom system (1 master and8 Subs), in robust plastic cabinets for desk or wallmounting. Call/talk/listen from Bader to Sabi andSubs to Master. Ideally suitable for Bushleaa, Sur-gery, Schools, Hospitals and Office. Operateson one 9V battery. On/off switch. Volume controlComplete with 3 connecting wires each 66ft. andother accessories. P.& P. 90p.

MAINS INTERCOM NEW MODELNo batteries -no wires. Just plug In the mainsfor instant two-way, loud and clear communication.On off switch and volume control. Price 133 74per pair P. & P. 90D.

NEW N I AMERICAN TYPE CRADLE

TELEPHONE AMPLIFIER

NLY

1495VAT El 20

Latest transistormed Telephone Amplifier withdetached plug -In speaker. Placing the receiver onto the cradle activates a switch for Immediatetwo-way conversation without holding the handset.Many people can listen at a time. Increase efficiencyin office, shop, workshop. Perfect for "conference"calls: leaves the user's hands free to make notes,commit files. No long waiting, eaves time withlong-distance calls. On/Off switch, volume. Directtape recording model at 116-96 + VAT 11.36P. P. 76p, 10 -day price refund guarantee.

WEST LONDON DIRECT SUPPLIES (E.L.6)169 KENSINGTON HIGH STREET, LONDON, WS

DENCO(CLACTON)

LIMITEDDept. E.E.

357-8-9 OLD RD., ,

CLACTON -ON -SEAESSEX C015 3RH

Our components arechosen by technicalauthors and con-structors throughoutthe world for theirperformance and re-liability, every coilbeing inspected twiceplus a final test and

near spot-on alignment.General Catalogue showing fullproduct range 34p. Overseas Cus-tomers 70p, Air -Mail Post Paid.

U.K. & OVERSEAS MANU-FACTURERS/STOCKISTS

ENQUIRIES WELCOME

Australian Readers Please Note -Our Complete -Range of Coils areavailable from Watkin Wynne Pty.Ltd., 32, Falcon Street, CROWSNEST, 2065, AUSTRALIA. P.O.Box 392.

TV GAMES CHIPAY -3-8500 £1150. Printed circuit and kit of extraparts £7.95. Add-on colour kit P.O.A. Send saefor free data.

NEW COMPONENTS SERVICEResistors 5% carbon E12 2.70 to 10M 1W 1p.1W 2p. Preset pots subminiature 0.1W E31001]to 4M7. Vertical 9p. Horizontal Op. Poten-tiometers 025W E3 4K7 to 2142 log or Iln. Single24p. Dual 75p. Polystyrene capacitors E12 63V22pf to 8200pf Sip. Ceramic capacitors vert. 50VE8 2201 to 47000pf 3p. Mylar capacitors 100V 001, -002, -005 4p. -01, 02, -025 Ofrp. Polyestercapacitors 250V ES 01 to 1mf 51p. 15, 22mt7p, 47mf 11p. Electrolytics 50V 47, 1, 2mf 5p.25V 5, 10mf Sp. 16V 22, 47mf Op. 100mf 7p. 220mfSo. 470mf 11p. 1000mf 16p. Zener diodes 400mWE74 3V3 to 33V alp.

MAINS TRANSFORMERS6-0-.0V 100mA 94p. 9-0-9V 75mA 94p. 18V IAE195. 0/12/15/20/24130V 1A £3-65. 12-0-12V 50mA94p. 0/12/15/20/24/30V 2A E4.95. 13.3V 11A f.210.6-0-6V 1,A £2-55. 9-0-9V 1A £2.19. 12-0-12V 1A42 49. 15-045V IA £2.69. 30-0-30V 1A L339.

PRINTED CIRCUIT KITS ETCContains etching dish, 100 so Ins of pc board,1 lb ferric chloride, etch resist pen, drill bit andlaminate cutter £365. 100 aci Ins pc board 75p.1 lb Fed 95p. Etch resist pen 75p.

S-DECS AND T-DECSS-DeC £1 94. T-DeC £3-61. i II Ifiru-DeCA £397.u-DeCB £697. 40114' 'IC carriers with s'iii -- - ie. .iNslitiesockets:- vaasq..........16 dli £1 91. 10T05 £1 79. yze

SINCLAIR CALCULATORS, WATCHESAND POCKET TVSinclair pocket TV £165. Cambridge Scientific0545. Cambridge Memory £5.95. Oxford Scien-tific E1060. Mains adaptors (State model) £320.

BATTERY ELIMINATOR BARGAINS3 -WAY MODELSWith switched output and 4 -way multi -lackconnector. Type 1, 3/41/6V at 100mA £230.Type 2: 6/71/9V 300mA £2110.100MA RADIO MODELSWith press -stud connectors. 9V £345. 6V £345.9V + 9V £545. 6V + 6V £5.45. 41V + 44V L545.CASSETTE MAINS UNIT74V with 5 pin din plug 150mA £365.FULLY STABILIZED MODEL £545Switched output of 3/6/71/9V 400mA stabilized.CAR CONVERTORS 12V INPUTOutput 9V 300mA E1 AN. Output 75V 300rnA £180

BATTERY ELIMINATOR KITSSend sae for free leaflet on range.100mA radio types with press stud batteryterminals. 45V £2.10. 6V £2 10. 9V L210. 401 +4)V £250. 6V + I3V £250. 9V + 9V £250.Cassette type 75V 100mA with din plug £210.Transistor stabilized 8 -way type for low hum3/41/6/75/9/12/15/18V. 100mA £320. 1 Amp C.I511.Heavy duty 13 -way types 45/6/7/81/11/13/14/17/2I/25/28/34/42V. 1 Amp £4115. 2 Amp £7415.Car convertor kit Input 12V DC. Output 6/75/9VDC IA transistor stabilized £1-9SStabilized Laboratory power kit Switched1 to 30V In 0 IV steps. lAmp £1245. 2 Amp £1405

SINCLAIR PROJECT 80 AUDIO MODULESPZ5 Ea 95. Z40 £5 75.BI-PAK AUDIO MODULESS450 tuner £20 95. ALSO £4 60. PA100 E14-95.MK60 audio kit C31-95. Stereo 30 £1550. SPME10E3 8S. BMT £3.32. Send sae for free data.

SINCLAIR IC20IC20 10W+10W stereo Integrated circuit amp kit

with printed circuit and data E495.PZ20 Power supply kit for above £3 -OS.VP20 Volume, tone control and preamp kit ELM.Send sae for free leaflet on the whole system.

./C12 AND JC40 AMPLIFIERSJC12 SW IC audioamp with free dataandcircuit EI95Also new JC40 20W --- almodel with pcbE395. Send sae for free leaflet on both modelsand associated power supply and preamp kits.

FERRANTI ZN414IC radio chip E1 44, Extra parts and pcb for radioE3115. Case £1. Send sae for free data.

SWANLEY ELECTRONICSDept E.E. PO BOX 68,32, GOLDSEL ROAD,

SWAN LEY, KENT BR8 8TQ.Mall order only. No callers. Send sae for free dataon kits. Post 30p on orders under £4.50, otherwisefree. Prices Include VAT. Official orders wel-come. Overtime customers deduct 7% on Itemsmarked and 11% on others.


B. BAMBER ELECTRONICS Dept. EE, 5 STATION ROAD, LITTLEPORT, CAMBS., CB6 11:1ETelephone: ELY (0353) 860185 (2 lines) Tuesday to Saturday

PLEASE ADD 8% VAT UNLESS OTHERWISE: STATED PLEASE ADD 8% VAT UNLESS OTHERWISE STATED

RED LEDIMin. type) 5 for 70p. MAINS ISOLATION TRANSFORMERS. Tappedmains input 2401, at 3A 12V at 500mA output.

VIDICON SCAN COILS (Transistor type, but no data) New, boxed, made by Gardners. E12.complete with vidicon base £6.50 aeon. Brand New.

GARRARD 9V DC MINIATURE MOTORS,FULL RANGE OF BERNARDS/ I ELEC.- Type 31BM. 3211, RPM governed, size approx.

11in. dia. x high, with 2mm spindle. BrandTHOR ICS ROOKS IN STOCK. SAE FOB LIST.sac

NEW FOR THE VHF CONSTRUCTOR. A range oftuned circuits on formers M. slugs and screening cans.frequencies quoted are approximate, and range can begreatly extended by using varying ...odors In parallel.Type S square, dumpy type).Type SA 20 to 30MHz (when 33$ fined in parallel).Type SIO 35 to 50MHz with link winding).Type SC 70 to 100MHz (with link winding).Type SO 135 to 175MHz (with link winding).Type M (Min. }in. square NU.).Type MA 19 to 28MHz (when 33pf fitted in parallel).Type MB 22 to 32MHz (when 33pf fitted In parallel).Type MC 25 to 35MHz (when 330 fined In petalled.Type MD 38 to 50MHz (when 330 fined In parallel).Type ME 45 to 80MHz (when 330 fined in Perelled.

30P1 SPECIAL OFFER ...lilSTARPHONE HIGH BAND RF PC BOARDS,

' with conversion data for making into a good 2MConverter. (All that is needed: 1 xtel, 7 caps.2 resistors, end 9V DC.) PCB contains 2 Dual pate

PLASTIC PROJECT BOXES with screw on lids (in Mos Fat RF stages 139140). Diode ring mixer.Black ABS) with brass inserts. 3 stage Osc/Multiplier. Alt on one PCB. approx. sizeTYPE NB1 approx. 310.0211n. x 111n. 40p amok. V 11", ext. connections, 9V DC supply. AGCTYPE N82 app.- 31In. x 211n. x 11in. SOP amok (can be left bias, or RF gain contro Arit.TYPE NB3 411n. x 31in. x 111n. 80p eralt. Mout, IF output (works from a few

Inover

30MHz). All Brand New. £6.50 each, while

MULLARD 85A2 85V STABIUSER VALVES stocks last.(13rend New) 70p each or 2 for £1.20.

Type MF 100 to 200MHz (without Slug) when 0 tovariable fitted in parallel.All the above coils imitable in pecks of five o

type) at SOP per peck of 5.

SILICON HIGH] VOLTAGE RECTIFIER STICKS,9Y185 (new) 35kV 2 5mA El each, BY140iex-equip) 12kV 2 5mA 45p each.

PERSPEX TUNER PANELS (for FM Band 2tuners) marked 88-108MHz and Channels 0-70,clear numbers, rest blacked out, smart modernappearance, size approx. 81in. x 1 lin., 2 for 35p.

PLUGS AND SOCKETSN -Type Plugs 50 ohm, 60p each, 3 for £1.50.PL259 Plugs IPTFEI, brand new, packed withreducers, 66p or 5 for E3.S0239 Sockets IPTFEI, brand new 14 -hole fixingtype), 50p each or 5 for £2.25.

VARIABLE STABILISED POWER SUPPLY,mains input 0-24V output, stabilised end currentlimiting :it 500mA 32V at 50mA. Brand new byBritish manufacturer Size approx. 71 x 21 z 4incomplete with external 5k0 3 -turn pot for voltageontrol. Connection data supplied. E7.

14 OIL REED RELAYS, 5 to 12V DC, 450 ohmcol:. Designed to work directly from TTL Logic.Single Pole Change over. Contact ratings 28V 1A13W. t1 .78 each.

TO3 transistor insulator sets, 10 for 50p.

2N3055 type Transistors. O.K., but unmarked,5 for El.

110V NEONS, SCREW -IN -TYPE, 4 for 50p.

BS)(20 (VHF OscJMultl, 3 for 513p.BC108 (metal cam. 4 for 50p.PBC108 (plastic BC108). 5 for 50pBEY51 Transistors. 4 for 60p.BCY72 Transistors. 4 for 50p.PNP audio type TO5 Transietors, 12 for 25p.BF 152 (UHF amp/rnixen. 3 for 50p.2N3819 Fet.. 3 for 60p.BC148 NPN SILICON, 4 to, 50p.

4MHz XTAL PACKS 110 assorted sta. between BC158 PNP SILICON, 4 for 50p. MULTICORE SOLDER4MHz and 5MHz/, our selection only. £1 Peck, BAY31 Signal Diodes, 10 for 35p. Size 5 Sevbit 18 s.w.g. in alloy dispenser, 32p

BAt 21 Vericap Diodes, 4 for 50p. VAT (3p).MINIATURE PLIERS. High quality "Crescent" Size CI SAV 18 Saybit 18 cw.g., 58p + VAT 140.made in USA. £4.35 +VAT (35p). SMALL MAINS SUPPRESSORS Ismail chokes, Size 12 Savbit 18 s.w.g. on plastic reel 01.80

ideal for radio. Hi-Fi Inputs, etc.). approx. 11n. x + VAT (15p).llin., 3 for SOp. i Kg. (1 11b11110 x 40, 20 s.w.g. on plastic reel C3.

A LARGE RANGE OF CAPACITORS AVAIL-ABLE AT BARGAIN PRICES, SAE. FOR UST.

MIXED COMPONENT PACKS, containingresistors. capacitors, pots, etc. All new. Hundredsof items. E2 per pack, while stocks last.

ALU-SOL ALUMINIUM SOLDER (made by Multi -core). Solders aluminium to itself or copper,bra., steel, nickel or tinplate, 16 s.w.g. withmulticore flux, with instructions. Approx. 1 metrecoil 40p pack. Large reel £2.75.

SOLDER SUCKERS (Plunger Type). Standard VARICAP TUNERS Mullard Type ELC1043/05.Model, £4.50. Skirted Model. E4.95. Spate Brand New £4.40 + 121% VATNozzles 80p each.SAROAIN PACK OF LOW VOLTAGE

WELLER SOLDERING IRONS ELECTROLYTIC CAPACITORS. Up to 50V

EXPERT. Built -in -spotlight illuminates work. Pistol working S""ni' APP"'' 100' °AI°grip with fingertip trigger. High effklency copper Per Pack 121% VAT.

soldering tip, Moblle Convene. 24V DC Input13 80 et

etc.) £9.80 +VAT (711p). battery).for running 120car radio lorry

EXPERT SOLDER GUN. CLIO VAT (54p1.EXPERT SOLDER GUN KIT (spare bite use. I(IZOX. 3 4A DC output fully stabilised. £3.60 each

SPARE BITS, PAIR, 30pF + VAT (2p).MARKSMAN SOLDERING IRONSSP15D 15W E3 VAT (24p).SP25D 25W E3 + VAT (24p).SP25DK 25W + bits, etc., kit £3.85 « VAT (31p).SP4OD 40W £3.44 VAT (28p).BENCH STAND with spring Marksman Irons.£2.22 VAT (18p).SPARE BITSMTB for 15W, 48p + VAT (4P).MT4 for 25W, 38p + VAT 13p),MT I0 for 40W 42p 0 VAT (3p).TCP2 TEMPERATURE CONTROLLED IRON.Temperature controlled iron end PSU £27 VAT(C2.161.SPARE TIPSType CC single flat, Type K double flat fine tip,Type P, very fume tip VI each . VAT (8p).

MOST SPARES AVAILABLE.

SIDE CUTTERS. High quality, £3.70 + VAT 30p.

We now stock Spiralux Tools for the electronicenthusiast. Screwdrivers, Nuts

SpatheBA and

Metric sizes, pop rivet guns. etc. SAE for list.

TWIN I.F. CANS, approx. tin. x }in. x 1 in, high,around 3 5-5MHz, 2 separate transforms. In1 can, Internally screened, 5 for 60p 12196 VAT.

Dubilier Electrolytics, 50pF. 450V. 2 for 50p.Dubilier Electrolytics, 100,A, 276V, 210r 50p.Plessey Electrolytics, 470pF, 83V, 3 for 50p.TCC Electrolytick 1000pF, 30V. 3 for 60p.Plessey Electrolytics, 1000$, 180V, 40p each13 for E11.Dubilier Electrolytics, 5000pF, 35V, SOp each.Dubilier Electrolytic', 5000pF, 50V, 60p each.ITT Electrolytice. 13800pF. 25V, high grade, screwterminels, with mounting clips, 50p each.Pie.. Electrolytical. t 0,000pF et 83V. 75p each.Plessey Cathodrey Capacitors, 0-0-4pF at 12 5kVDC. Screw terminals. £1.50 each.PLEASE ADD 123% VAT TO ALL CAPACITORS.

TV PLUGS AND SOCKETSTV Plugs (metal type). 5 for 60p.TV Sockets (metal type). 4 for 50p.TV Line Connectors (back -to -beck sockets/. 4 for 60p.Mamas add 124.% VAT.

Terms of Business: CASH WITH ORDER. MINIMUM ORDER f2. ALL PRICES INCLUDE POST & PACKING (UK ONLY) SAE with ALL ENOUIRIES PleasePLEASE ADD VAT AS SHOWN. ALL GOODS IN STOCK DESPATCHED BY RETURN. CALLERS WELCOME BY APPOINTMENT ONLY

First of course you need our catalogue -all200 pages of itl It's so packed with goodthings that it's known as the constructor's'Bible'. It costs just £1 plus 40p for post andpacking. With it comes a free Bargain Listshowing many items at such knock -downprices that the savings can pay for the cata-logue several times over. Send for a cataloguetoday, using the coupon on the right.

A wisemove -

Parr 71/6cOUPON

withOr P.O.

1.1'40

hn cooking up a newelectronic masterpiece/

I'm off to HomE RADIO nowo buy the components-.

During the many years we've been serving the needs ofradio and electronic constructors we've seen quite a fewodd customers at our Mitcham shop, but we must admitwe've not yet had a Chinese buffalo boy. However, evensuch a customer wouldn't really surprise us, for we getan amazing variety of characters, all having a commonenthusiasm for this ever-growing hobby. They come tous knowing they can choose from a wonderful stock ofcomponents. They know too they'll get that extra bit of'service' that makes all the difference. Of course, apartfrom those who call at our shop we have thousands offaithful customers who order regularly by post, havingchosen their components from our famous catalogue.Why not join them?

rPlease write your Name and Address in block capitals

HOME

NAME

ADDRESS

Is

RADIO (Components) LTD. Dept. EE214240 London Road, Mitcham, Surrey CBI 3140

4154

IRegn N. ILondon 9129661 j

HOME RADIO (Components) LTO. Dept. E.E., 234 -240 London Road Mitcham,CR4 3HD Phone 01-648 8422

Published approximately the third Friday of each month by IPC Magasinea Ltd., Fleet. oy Howe, FerrIngdon St., London EC4 4AD. Printed In England by Index Printer. Ltd., DunstableBeds. Bole Agents for Australia and New Zealand -Gordon and Gotch (Allis) Ltd. South Africa -Central News Agency Ltd. Everyday Electronics is sold subject tothe following conditionsnamely that it shall not, without the written consent of the Publishers first given, be lent, resold, hired ont or otherwise disposed of by wayof Trade at more than the recommended sellingprice shown on cover, excluding Eire where the selling price is subject to V.A.T., and that It shall not be lent, resold, or hired out or otherwise disposed of In a mutilated condition or in

Any unauthorised cover by way of Trade, or edited to or as part of spy publication or advertising, literary or pictorial matter whatsoever.

SEMICONDUCTORS -COMPONENTSDIODES

Type Price Type Price Type PriceAA129 £0.08 BY100 £0.16 BYZ11 £0 31 0A91 £0 07AAY30 £0.09 BY107 £0.12 BYZ12 £0 31 OA95 £0 07AAZ13 £0.10 BY105 £0.18 BYZI3 £0.26 0A182 £0.07AAZI7 £0.10 BY114 £0.12 BYZ16 £0 41 0A200 £0 08BA100 £0.10 BY124 .£0,12 BYZ17 £0 36 0A202 £0.08BAI02 £0.32 BY126 .£0.15 BYZ18 £0 36 SD10 £0 06BA148 £0-15 BY127 BYZI9 £0.28 SD19 £0'06BAt 54 £0-12 BY128 .£0.16 0A10 £035 N34 £0 07BAI 55 £0-14 BY130 .£0.17 0A47 £007 N34A £0 07BA156 £0-14 BY133 '£0.21 0A70 £0.07 N914 £0 06BA173 £0.15 BY164 £0.51 0A79 £0 07 N916 £0 06BB104 £0.15 BY176 .£0.75 0A81 £0 07 N4148 £0.06BAX13 £0.07 BY206 £0.00 0A85 £0.09 S44 £0 05BAX16 £0.08 BYZIO £0.36 0A90 £0 07 S920 £0.06

SILICON RECTIFIERSType Price Type Price Type Price Type PriceS920 £006 N4003 £0.07 S020 £0-10 S031 £0 25S921 £0.07 N4004 £0.08 5021 £0-11 f45400 £0.135922 £0.08 N4005 £0.09 S023 £0-13 N5401 £0 15S923 £0.09 N4006 £0.10 S025 £0-14 N5402 £0-16S924 £0.10 N4007 £0.11 5027 £0.16 N5404 £0.17N4001 £0-05 5015 £0.09 S029 £0.20 N5406 £0 21N4002 £0.06 N5407 £0.25

TRIACS2 AMP TO5 CASE

Volts No. Price100 TRI2A/100 £0.31200 TRI2A/200 £0.51400 TR12A/400 £0.71

10 AMP TO48 CASEVolts No. Price100 TR110A/100 £0.77200 TR1I0A/200 £0.92400 TR110A/400 £1.12

6 AMP TO66 CASEVolts No. Price100 TRI6A/100 £0 51200 TR16A/200 £061400 TR16A/400 £0.77

10 AMP TO48 CASEVolts No. Price100 TR110A/100 £0.77200 TR110A/200 £0.92400 TR110A/400 £1-12

SUPER UNTESTED PAKSPak OrderNo. Qty. No, PriceU50 100 Germ. gold bonded 0A47 diode 16130 £0.60U51 150 Germ. 0A70/81 diode 16131 £0.60U52 100 Silicon diodes 200mA 0A200 16132 £0.60U53 150 Diodes 75mA 1 N4148 16133 £0.60U54 50 Sil rect top hat 750mA 16134 £0.60U55 20 Sil red stud type 3 amp 16135 £0 60U56 50 400mW zeners DO7 case 16136 £0 60U57 30 NPN trans BC107/13 plastic 16137 '£060U58 30 PNP trans BC177/178 plastic 16138 '£0.60U59 25 NPN T039 2N697/2N1711 silicon 16139 £0.60U60 25 PNP T050 2N2905 silicon 16140 £0 60U61 30 NPN T018 2N766 silicon 16141 £0 60U62 25 NPN BEY50/51 16142 £0 60U63 30 NPN plastic 2N3906 silicon 16143 £0.60U64 30 PNP plastic 2N3905 silicon 16144 .£0.60U65 30 Germ. 0071 PNP 16145 £0.60U66 15 Plastic power 2N3055 NPN 16146 £1'20U67 10 TO3 metal 2N3055 NPN 16147 £120U68 20 Unijunction trans 11543 16148 £0.60U69 10 1 amp SCR T039 16149 £1.20U70 8 3 amp SCR TO66 case 16150 £1-20Code Nos. mentioned above are given as a guide to the type ofdevice in the pak. The device themselves are normally unmarked.

LINEAR PAKSManufacturer's ''Fall Outs" which includeFunctional and part -Functional Units.These are classed as "out of -spec" fromthe maker's very rigid specifications, butare ideal for learning about ICs and ex-perimental work.U721-30 Assorted Linear Types, 709 741,747, 748, 710, 588, etc.

ORDER No. 16227 .£1.50U76SD FM STEREO DECODER5 ICs 76110 equivalent to MC1310P-MA767.Data supplied with pak.

ORDER No. 16229 .£1-50U76A AUDIO POWER OUTPUTAMPLIFIERS8 assorted types. SL403, 76013, 76003, etc.Data supplied with pak.

ORDER No. 16228 .£100

THYRISTORS600mA TO18 CASE 7 AMP TO48 CASE

Volts No. Price Volts No. Price10 THY600/10 £0.13 50 THY7A/50 £0 4820 THY600/20 £0.13 100 THY7A/100 £0 5130 THY600/30 £0 19 200 THY7A/200 £0 5750 THY600/50 £13-22 400 THY7A/400 £0 62

100 THY600/100 £0.25 600 THY7A/600 £0.78200 THY600/200 £0.38 800 THY7A/800 £0-92400 THY600/400 £0 45

1 AMP TO5 CASEVolts No. Price50 THYI A/50 £0.26

100 THYIA/100 £0,27200 THY1A/200 £0'28400 THYI A/400 £0.36600 THYI A/600 £0.45800 THY1A/800 £0.58

10 AMP TO48 CASEVolts No. Price50 THY10A/50 £0.51

100 THY10A/100 £0.57200 THY10A/200 £0.62400 THY10A/400 £0 71600 THY10A/600 £099800 THY10A/800 E1 22

3 AMP TO66 CASEVolts No. Price50 THY3A/50 £0.25

100 THY3A/I00 £0.27200 THY3A/200 £0-33400 THY3A/400 £0-42600 THY3A/600 £050800 THY3A/800 £0.65

16 AMP TO48 CASEVolts No. Price

50 THY16A/50 £0.54100 THY16A/I00 £0.58200 THY16A/200 £0 62400 THY16A/400 £0.77600 THY16A/600 £0 90800 THYI6A/800 £1.39

5 AMP TO66 CASEVolts No. Price50 THY5A/50 £0-36

100 THY5A/100 £0 48200 THY5A/200 £0.50400 THY5A/400 £0 57600 THY5A/600 £0.69800 THY5A/800 £0'81

30 AMP TO94 CASEVolts No. Price50 THY30A/50 £1 -18

100 THY30A/100 £1.43200 THY30A/200 £1 -63400 THY30A/400 £1.79600 THY30A/600 £3-50

COMPONENT PAKSPakNo. Qty.Cl 200 Resistor mixed value approx.

(count by weight)C2 150 Capacitors mixed value approx.

(count by weight)C3 50 Precison resistors. Mixed

valuesC4 80 1W resistors mixed preferred

valuesC5 5 Pieces assorted ferrite rodsC6Cl 1

2 Tuning gangs. MW/LW VHFPack wire 50 meters assorted

colours single strandC8 10 Reed switchesC9 3 Micro switchesC10 15 Assorted potsC11 5 Metal jack sockets 3 x 3.5mm

2 x standard switch typesC12 30 Paper condensers preferred

types mixed valuesC13 20 Electrolytics trans. typesC14 1 Pak assorted hardware-

nuts/bolts, gromets, etc.C15 5 Mains slide switches ass.C16 20 Assorted tag strips and panelsC17 15 Assorted centre: kr,obsC18 4 Rotary wave change snitchesCI9 2 Relays 6-24V operatingC20 1 Pak. copper laminate approx.

200 sq.in.C21 15 Assorted fuses 100mA-5 ampC22 50 Metres PVC sleeving assorted

size and colourC23 60 1 watt resistors mixed preferred

valuesC24 25 Presets assorted type and valueC25 30 Metres stranded wire assorted

colours

OrderNo. Price16164 .£0.60

16165 .E0 60

16166 £0 60

16167 0E0.60

16168 .£0 6016169 .£0 6016170 £0 60

16171 '£0.6016172 .£0 6016173 .£0 6016174 .£0 60

16175 *£0 60

16176 .£11 6016177 £0 60

16178 '£0.6016179 £0 6016180 .£0 6016181 .£0 6016182 .£0 6016183 £0 60

16184 £0.6016185 £0.60

16188 .£0 60

16186 .£0-6016187 £0.60

74 SERIES PAKSManufacturer's "Fall Outs" which includeFunctional and part -Functional Units.These are classed as "out -of -spec" fromthe maker's very rigid specifications, butare ideal for learning about ICs andexperimental work.74G-100 Gates assorted 7400-01-04-10-50-60, etc.

ORDER No. 16224 £12074F-50 Flip -Flops assorted 7470-72-73-74-76-104-109, etc.

ORDER No. 16225 £1.2074M-30 MSI. Assorted Types. 7441-47-90-154, etc.ORDER No. 16226 £1.20

VEROBOARDS PAKSVB1-Approx. 30sq.in various sizes. All0.1in matrix.

ORDER No. 16199 60pVB2-Approx. 30sq.in various sizes. 0 '15inmatrix.

ORDER No. 16200 60p

ELECTROLYTIC PAKSA range of paks each containing 18 firstquality, mixed value miniature electroly-tics.ECI-Values from 0.47µF to 10µF.

ORDER No. 16201 60pEC2-Values from 10oF to 1004F.

ORDER No. 16202 .60pEC3-Values from 1004F to 680µF.

ORDER No. 16203 60p

C280 CAPACITOR PAK75 Mullard C280 capacitors, mixed valuesranging from 0.01/oF to 221./F complete withidentification sheet.

ORDER No. 16204 .£1.20

SLIDER PAKSPakNo. Qty.St 6 Slider potentiometers, mixed valuesS2 6 Slider potentiometers, all 470 ohmsS3 6 Slider potentiometers, all 10k 02 linS4 6 Slider potentiometers, all 22k 11 linS5 6 Slider potentiometers, all 47k G linS6 6 Slider potentiometers, all 47k ft log

OrderNo.161901619116192161931619416195

Price

.£0-60£0.50

.£0 60

.£0 60

5 AMP TO220 CASEVolts No. Price400 THY5A/400P £0-57600 THY5A/600P £0.69800 THY5A/800P £0.81

No. PriceBT101/500R £0.80BTI02/500R £0.80BT106 £1.25BT107 £0.93BT108 £0.982N3228 £0.702N3525 £0'77BTX30/50L L0.33BTX30/400L £046C106/4 £0 60

ORDERINGPLEASE WORD YOUR ORDERSEXACTLY AS PRINTED, NOTFORGETTING TO INCLUDE

OUR PART NUMBER

VATADD 12+% TO PRICES MARKED*ADD 8% TO OTHERS EXCEPTINGTHOSE MARKED t, THESE ARE

ZERO RATED

CERAMIC PAKContaining a range of first quality miniature ceramic capacitors.Unrepeatable value.Pak OrderNo. Qty. No. PriceMC1 24 miniature ceramic capacitors, 3 16160 *£0-60

of each value-22pF, 27pF,33pF, 39pF, 47pF, 68pF, and82pF

MC2 24 miniature ceramic capacitors, 3 16161 *E0 60of each value-100pF, 120pF,150pF, I 80pF, 220pF, 270pF,330pF and 390F

MC3 24 miniature ceramic capacitors. 3 16162 .£0.603 of each value-470pF , 560pF,680pF, 820pF, 1,000pF, 1,500pF2,200pF and 3,300pF

MCA 21 miniature ceramic capacitors, 16163 .£0.603 of each value-4,700pF, 6,800pF0.01µF, 0.015uF 0.022/./F.0.033gF and 0-0470F

Just a selection from ourhuge stocks!

SEE OUR1977 CATALOGUE126 pages packed with

valuable informationORDER NOW

ONLY 50pplus 15p p & p

CARBON RESISTOR PAKSThese paks contain a range of CarbonResistors, assorted into the followinggroups:R1-60 mixed 1W 100-820 ohms.

ORDER No. 16213 ''60pR2-60 mixed 1W 1-8-2110.

ORDER No. 16214 '60pR3-60 mixed 1W 10-82k22.

ORDER No. 16215 *60pR4-60 mixed 1W 100-8205f2.

ORDER No. 16216 .60pR5-40 mixed 1W 100-82012.

ORDER No. 16217 .60pR6-40 mixed 1W 1-8-2k12.

ORDER No, 16218 60pR7-40 mixed 1W 10-82k22.

ORDER No. 16219 60pR8-40 mixed 1W 100-820k0.

ORDER No. 16220 60pR9-60 mixed 1W 1-10MG.

ORDER No. 16230 '60pR10-40 mixed 1-W 1-10M0.

ORDER No. 16231 60p

WORLD SCOOP JUMBOSEMICONDUCTOR PAK

Transistors, Germ. and Silicon Rectifiers,Diodes, Triacs, Thyristors, ICs andZen ers.

ALL NEW AND CODEDApprox. 100 pieces. Offering the amateura fantastic bargain PAK and an enormoussaving -identification and data sheet Inevery pak.

ORDER No. 16222 £2.25

Dept. E.E.6, P.O. Box 6, Ware, HertsCOMPONENTS SHOP: 18 BALDOCKSTREET, WARE, HERTS

The only organ you can build in stages andtailor to your requirements as you goalong-and at each stage you'll have a fullyworking instrument! We haven't got thegimmicks (yet-they're coming soon), but wehave got the most beautiful sounds-youwon't find them on any organ less than twiceour price. So get our MES50 series leafletsnow! 65p buys the three available so far.

We stock a wide range of switchesincluding a really low-priced highquality interlocking push-buttonswitch system, which is extremelyversatile. We've got toggleswitches, slide switches, pushswitches, rotary switches-thereare dozens to choose from, but it'sonly a tiny part of our fantasticrange.

Our bi-monthly newsletter keeps you up to date with latestguaranteed prices - our latest special offers (they save youpounds) - details of new projects and new lines. Send 30pfor the next six issues (5p discount voucher with each copy).

MAPLIN ELECTRONIC SUPPLIESP.O. BOX 3 RAYLEIGH ESSEX SS6 8LR

Telephone: Southend (0702) 715155Shop: 284, London Road, Westcliff-on-Sea, Essex

(Closed un Monday) Telephone. Southend (0702147379

This high quality Graphic Equaliser will enhance even the mostsophisticated system at a fraction of the cost of a ready-madeequaliser of equal quality. You can get all the parts from us(except woodwork) including drilled and printed metalwork.Construction details in our leaflet: 15p.

A completely self-contained pedalunit. 13 -note, 2 -octave range,4 organ stops. It can be added toany organ! A really unusual extrais the bass guitar stop which usesfour envelope shapers to give areal bass guitar sound. A must forthe solo guitarist. Full constructiondetails in our catalogue-post thecoupon below now!

Play fascinating games NOW onyour own 1.v. in your own livingroom. The kids will think it's magicwhen the scores pop up on thescreen. Lay your bets-anyonecould win-with Maplin's priceseveryone can win. All parts atremarkably low prices (I.C. alone£11 99)., send for our latestnewsletter for details. All pricesinclude VAT and Pt, P.

Complete Kit £24.50. Please add 3pto Kitprice for copy ofconstructional details.

IT'S A FANTASTIC BESTSELLER!. 216 big (11" x 8") pages! Over a thousand illustrations!

Over 30 pages of complete projects to build!Thousands and thousands of useful components describedand illustrated! No wonder it's a bestseller!DON'T MISS OUT! SEND 50p NOW!r

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Please rush me a copy of your 216 page catalogue by return of post.I enclose 50p, but understand that if I am not completely satisfied I mayreturn the catalogue to you within 14 days and have my 50p refundedimmediately.

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Construction and theory for everyone even/day tEP 7 7 ...

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