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MIRAMAR INDSHORT WAVE Malin

THIRDEDM011

TCII CIISTS TM COPY

. . . This edition of the Hammarlund Short -WaveManual, proofs of which you have sent me, looks excel-lent. It should be extremely interesting to anyone inter-ested in building sets for short-wave work. Knowing, asI do the history of most of the set designs given andthe manner in which they are described, I can heartilyendorse them for the set builder.-L auronce 3l.(..mkatiav, Editor, Radio News.

. . . After having been permitted to look over theproofs of the new 1936 Hammarlund Short WaveManual, I certainly feel that the Hammarlund Manu-facturing Company has outdone itself in giving theshort wave experimenter and builder a Manual thatis outstanding in all respects.

. It provides sufficient variety to suit all tastes andgives more than the usual amount of information sonecessary to the earnest short wave constructor whocan never get too much of such help. The new Manualshould be treasured by all those who are fortunateenough to obtain one.- Hugo Gorrzsbark, Editorcrud Publisher of Radio Craft, Short Wave &Television. etc.

. . . Every well-known national radio magazine hascontributed some worth -while contribution to the artin the form of a modern, simple short-wave receiver.The magazine technical staffs vie with each other forthe honors. But in the Hammarlund Short Wave Man-ual you find the most important contributions from allof these radio magazine experts. Thus this Manualbrings you, under one cover, +he complete descrip-tions of everything that is best in short-wave receiverdesign. There is not a receiver description in this Man-ual which is not a top-notcher.-I1. W. Dielcou:. Pub-lishcr of "The Radio Handbook."

TheHammarlund 1936

Short Wave ManualIMM

THIRD EDITION

AN AUTHENTIC HIGH

FREQUENCY GUIDEFOR THE AMATEUR,EXPERIMENTER, AND

LISTENER -IN

THE HAMMARLUND MANUFACTURING CO., Inc.424-438 West 33rd Street, New York, N. Y.

Edjlion fully Copyrighted 1935. Hiunniarluod Mfg. Ca.. Ine. Printed io

IntroductionT N this manual will be found the con-' structional details on what is, probablythe most carefully selected and compre-hensive group of inexpensive short-wavereceiver designs ever published in asingle volume.

The selections were made by the ed-itors of five of the leading radio publica-tions of the United States from amongthe most popular and efficient designsdescribed in their publications during thepast year or so. Then models of the re-ceivers were constructed and put throughtheir paces in the laboratory and "on theair" with the result that the thirteen de-signs presented here represent the creamof the hundreds offered to the home con-structor during past months.

Inasmuch as the most popular designsare the more simple ones that combinelow cost with efficiency, the receivers de-scribed here naturally fall in that class.The requirements of the constructor whois looking for more advanced design arenot overlooked however. Then, too, whilethe demand is greatest for short-wavebroadcast receivers, the special require-ments of receivers for operation on theamateur bands have not by any meansbeen neglected as is indicated by thefact that band -spread designs and even a5 -meter receiver have been included inthis group.

Having arrived at the final selection ofreceivers, the next step was to turn themodels over to the experimental labora-tory for careful study to determinewhether any of them could in any waybe improved. The fact that several ofthem carne out of this laboratory withimprovements should not be taken as areflection on the original designers orthe publications in which the originaldescriptions appeared. The changes mademainly took the form of substitution ofmore modern tubes or more efficientcoils, with some changes in associatedparts to adapt them to these new units.In a few other instances changes whichbrought about a considerable improve-ment in efficiency at a slight increase inparts cost were considered justified andwere therefore made.

In some respects reception of shortwave signals differs considerably from re-ception of signals on the broadcast bandabove 200 meters. Perhaps the most prom-inent difference is found in the aston-ishing distances that can be covered witheven the most simple one or two

tube receivers. It is no particular feat,for instance, to hear the European sta-tions and others from remote parts of theglobe quite regularly with such receivers.

Such distance reception is not limitedto the hours of darkness, as is DX re-ception on the broadcast band. In factsome of the most phenomenal receptionis obtained in the daytime.

Generally speaking the larger the wave-length, the later in the day will best re-ception occur. The 16 meter broadcaststations, for instance, are best during themorning hours. Those operating on 10meters come in well during the latemorning and early afternoon hours. The25 and 31 meter stations usually are heardwith maximum volume during the lateafternoon and early evening hours andthose on 50 meters are best received afterdarkness has fallen.

The foregoing holds true with few ex-ceptions in North America. One of theseexceptions is reception from Australianstations. These operate around 31 meters,yet are heard best by Americans in theearly morning before breakfast (at whichtime it is evening in Australia and NewZealand).

There are explanations for the condi-tions mentioned, some of them beingrather involved. However, the importantthing, from the standpoint of the short-wave listener, is that these conditions doexist. They mean that the old practiceof sitting up all night for good DX re-ception is a thing of the past, and thatpractically any waking hour is a goodone for foreign DX reception, on onewave -length or another in the short-waverange.

Tuning a short-wave receiver is a farmore critical business than is the sameoperation on the broadcast band. This isnot due to any electrical peculiarities in-herent in the short waves and is best ex-plained by an arithmetical example.

Assume that a receiver is capable ofseparating stations which are broadcast-ing at frequencies 10 kilocycles apart. Inthe broadcast hand of 1500 to 550 kc.there would be room for 96 such stationchannels. If the tuning dial were prop-erly marked off in 96 divisions therefore,a station would be heard at every divi-sion on this dial.

Now, going down to the short -waves,the tuning range of a single coil may befrom 20 meters to 50 meters which means,in terms of frequencies, from 15,000 kc.

The HAMMARLUND 1936 SHORT WAVE MANUAL 3

to 6,000 kc. Instead of providing for 96channels there would be 900 such 10kilocycle channels and with the samedial marking as mentioned above, therewould be 10 channels to every divisionof the dial instead of only one. It there-fore follows that in tuning the short-wavestations the adjustment of the dial hasto be exact to a small fraction of a di-vision. A high ration tuning dial is oneway of accomplishing this.

Undoubtedly the most practical methodis found in the use of some sort ofband -spreading system. The most com-mon of these is the one in which a smallvariable condenser is connected directlyacross the regular tuning condenser, thesmall condenser being employed for theexact tuning. Take as a specific examplea short-wave receiver with a coil pluggedin which covers the range of 20 to 50meter- mentioned above, and employinga tuning condenser of 140 timid. max-imum, capacity. Rotating his condenserthrough its entire capacity range tunesthe receiver through a frequency rangeof 15.000 to 6000 kc., a span of 9000 Ice.or 900 10-kc. channels. Now, suppose ashunt variable condenser of much smallercapacity is placed across this 140 rumfd.condenser. Swinging this small condenserthrough its entire range will result in arelatively small capacity variation andtherefore a relatively small frequencyrange. With the selection of the propersmall capacity, for instance, the frequen-cy range with the smaller condenser maybe only 1/10th as great as with the largercondenser and in such a case there wouldbe only 90 channels within the range ofthis condenser, and tuning would becomeas non -critical as that in the averagebroadcast receiver.

When this system is employed no ad-ditional coils arc required and the onlyextra cost is that of the small condenser.The large condenser is employed to tunethe receiver into the particular band de-sired, say the 25 meter broadcast band.For instance, then the small condenser isemployed to tune in the stations withinthat hand. These stations will then bespread out over perhaps 15 or 20 de-crees on the hand -spread dial whereasthey would fall within 1 or 2 degrees iftuned on the dial of the larger con-denser alone.

Variable condensers, such as the Ham-marlund Type MC -120B, are availablewhich are especially intended for par-allel band -spread use. These are madewith the 2 condenser sections combinedin a single unit but with separate shafts.These condensers are principally usedin "ham" receivers.

For those who are interested in a more

detailed study than that presented here,an interesting discussion of band -spread-ing methods, analyzing the variousmethods in considerable detail, will befound in the October, 1934 issue of"Radio News."

There is a considerable difference inopinion as to what constitutes the mostdesirable type of receiver for short-wavework. There are many who prefer the.

POPULAR JAPANESE SHORT WAVETRANSMITTER

The station which is heard the worldover and is the goal of listeners.

modern superheterodyne and a host thatswear by the regenerative receiver.

There is much to be said for bothtypes of receivers. Where a single re-ceiver is required to cover both theshort-wave and broadcast bands, thesuperheterodyne receiver undoubtedlyhas the edge because of its superior se-lectivity on the broadcast hand. Forpurely short-wave work it can safely besaid that either of these general types ofreceivers, if well designed and con-structed, is capable of excellent service.

Among those who "build their own"the regenerative type of receiver is by farthe most popular. It is less costly, easierto build, more easily understood by thenovice and more economical in currentconsumption. Its selectivity may notequal that of a good superheterodyne,but it is selective enough for most pur-poses. Its sensitivity is as great as canhe used in many locations-enabling it tobring in any signals that are above thylocal noise level of the average location.

No mention has been made of eitherstraight tuned r. f. receivers, or thoseemploying super -regeneration, becauseneither one of these rates serious con-sideration for general short-wave workbetween 15 meters and 200 meters.

Super -regeneration is without a rivalfor use in inexpensive receivers to oper-ate on wavelengths below 10 meters be-cause at these extreme frequenciesneither tuned radio -frequency amplifica-tion nor normal regeneration are useful.

4 The HAMMARLUND

SHORT WAVE FANS IN JUNGLES OFMALACCA

A group of Jungle Dwarfs (the Sakai)tuning in on a short wave regenerativereceiver brought to them by Frank Buck.The variable condensers, sockets, coils,

etc. are all HAMMARLUND.If the signal voltage of a distant sta-

tion is only in the neighborhood of a fewmillionths of a volt (as is very oftenthe case) at the antenna it is obviousthat losses or inefficiency of any kindmay make it quite impossible to hear thatsignal. Whether one's personal prefer-ence is for a superheterodyne or a re-generative receiver, therefore, the mostimportant single factor in the success ofthe receiver, outside of the choice of agood design to follow, will be the careexercised in selecting the parts.

Sonic points of inefficiency are gener-ally recognized. In the mattes of insu-lation, for instance, the average short-wave enthusiast has learned that nothingshor of the best is good enough. Thisexplains the almost . -ersal preferencefor Isolantite insulated tuning condensersand roil sockets. There are, however,other factors which are less often con-sidered. Perhaps the most important ofthese is the pine -in coil.

A recent study of the low and medium-priced plug-in coils available on the openmarket showed them to have an average"Q" of approximately 100 (at 15 mega-cycles) whereas the "Q" of a perfect roilshould approximate 200. Inasmuch as"Q" represents the efficiency of a coilin a tuned circuit, the implication ofthese figures is obvious. In actual prac-tice, a "Q" of 200 is not obtainable inpractical plug-in coils because of certaininherent losses introduced by the metalprongs of the coil form, or metal nearthe coil when in position in the receiver.

Hammarlund has made high-grade plug-in coils for years, but the,e have beenbeyond the purse of the average setbuilder. However, after a careful in-

vestigation, the conclusion was reachedthat plug-in coils of excellent character.istics could be produced to sell at a lowprice, especially as h of the researchand development work involved in suchan effort had already been accomplishedin producing the coils employed in theHammarlund "Pro" receivers. The de-sign work was therefore started and thenew coils are now on the market at thesame price as ordinary coils. The formsemployed in these new coils are mouldedof XP -53, an exclusive Hammarlund pro-duet developed for this purpose. In thisnew insulating material the losses havebeen reduced to a point where it closelyapproaches the low -loss characteristics ofthe most expensive dielectric materials.Even the use of artificial coloring hasbeen avoided, leaving the material anatural light tan. In production, thesecharacteristics are scrupulously main-tained and even improved by mouldingthe XP -53 in a groove ribbed shape toreduce the contact area between wind-ing and form to a mini r.

As matters of utility and convenience,the coil forms are hied with an in-side shoulder which permits mountingthe new Ha lllll larlund type APC trimmingcondensers within the form, as illustratedbelow, where they are required for spe-cial hand -spread or "fixed tune" purposes.A generous rim is provided at the topedge of the form, making it easy tograsp, and a removable wavelength indexcard is provided at the top of the form,on which the range of the coil is printed.Where forms alone are purchased, forwinding coils at home, these index cardsare left blank so that the builder canwrite in the range of the finished coil.

The development of the roil form was.

APC MIDGET IN XP -53 FORMA cutaway view of the new XP53 HAM-MARLUND coil form with the popularair padding condenser, type APC, mount-

ed on the special threaded shelf.

1936 SHORT WAVE MANUAL 5

HAMMARLUNI) SHORT Q AVERADIO ON THE MORRISSEY

()scar Hammarlund (left) at the cotrolsof a Hammarlund "Pro" with Capt. BobBartlett looking on. on board the Mor-

rissey, the North Pole schooner.

of course, only one step in the processof design. The design of the windingsfor the various frequency ranges repre-sents the real achievement of the en-gineers. The first step in this work wasto determine the most practical frequencyranges for each coil-not in an effort torover as niuch of the short-wave band aspossible with each coil hut to determinethe required range for each coil in itsrelationship to the important short-wavestations. It is a well established fartthat the greatest short-wave tuning effi-ciency is obtained when the coil induct-ance is such that relatively little tuningcapacity is required to tune the coil tothe desired frequency. The problem,therefore, was to allocate the ranges sothat as many as possible of the importantfrequency bands could be tuned at rela-tively low capacity values. The bandsaimed at primarily were the 19, 25, 31and 49 meter broadcast bands and the20, 40, /10 and 160 meter amateur bands.In the final coils all of these are tunedwith highly favorable capacity ratio. Atthe same time ample overlap is providedbetween ranges. The entire band from17.5 meters up to. and including approxi-mately, one third of the regular broad-cast band is covered with a set of hoarcoils, using a 140 tnmf. Hammarlundcondenser, as follows:

Coil 1-17,100 ke. to 7,300 kc. (17.5to 41 meters).

Coil 2-9,200 kc. to 4,000 kc. (32.6to 75 meters).

Coil 3-4,500 kc. to 2,000 kc. (66.6to 150 meters).

Coil 4-2,200 kr. to 1,100 kc. (136to 270 meters).

hi addition to the above coils, a sep-arate coil is available to rover the bal.

ance of the broadcast band. This coil hasa range of 1;200 to 535 kr. or 250 to 560meters. An additional coil is also avail-able to cover the ultra high frequencyrange of 30,000 to 15,000 kc., or 10 to 20meters.

It is well to point out here that theabove frequency ranges were measuredunder actual operating conditions, withthe coil plugged into a typical band -spread (parallel condenser) receiver andthe antenna connected. If anything theseranges are conservative because the testreceiver was completely shielded and theproximity of the shield walls would tendto reduce the coil ranges at the high -frequency ends. This is important be-cause it means that the builder of a re-ceiver can depend on these coils coveringthe ranges specified.

Having determined the approximateranges for the coils, there were left thenumerous other factors for study, such asthe best form factor, the best wire sizesand spacing, the best positions for thecoils on the forms and the spacing be-tween windings. Most of these vary withfrequency and therefore each individualcoil represented a separate problem in itself.

Space does not permit going into moredetail here but the final proof of the ex-tellence of these coils is found in thefart that the "Q" (al 15 megacycles) wasfound to exceed 150. This is believed tohe the highest value of efficiency obtain-able in plug-in coils of conventional type.

Finally, the prong connection arrange-ment is worthy of mention. There havein the past been no standards as to whichprong should be the control -grid con-nection, which the plate, etc., in any but4 -prong coils; and even in these thestandard was not definite. Now, throughthe efforts of some of the n lllll ufacturers

REMOTE SHORT WAVE WORKSports and other remote broadcasts aresent to the main transmitter by portableshort ware equipment as shown. Note the

antenna-a loop of tubular copper

6 The HAMMARLUND

SHORT WAVING FROM AEROPLANESA radio operator talking to his home

oflice by way of short waves.

and of the magazine "Radio News" an at-tempt is being made to standardize theseconnections. The standards proposed todate have been adopted in these Ham-marlund coils.

Proper attention and forethought inplanning the layout and wiring is essen-tial if a short-wave receiver is to prove

This is particularly true of theparts involved in the tuned circuit of thedetector (and the r. f. tube if one isused). The coil should be placed a dis-tance at least equal to its radius fother parts such as the tuning condenser,tube shields, metal panels, metal chassis,etc. Otherwise such metal masses will se-riously reduce the efficiency of the coil.The coil, the tube and the tuning con-denser should, except for this limitation,he placed as close together as practicalin order that all wiring of the grid andtuned circuits will be as short as possi-ble. Then this wiring should be run instraight lines-avoiding right-angle bends,as one would the plague.

A metal panel or chassis should not bedepended upon as a conductor for r. f.circuits. All r. f. connections should bemade by means of wires, and these wiresall connected together at one point ofthe metal chassis or panel.

One part of the average short-wave re-ceiver that receives too little attentionis the r. f. filter in the plate circuit ofthe detector. Unless a really good filteris used here the r. f. currents get intothe headphones or into the audio ampl;-fier where they tend to increase bodycapacity effects, cause instability and mayeven make it difficult to obtain properregeneration. A filter consisting of tworhokes connected in series and with

.00025 mfd. by-pass condensers, one con-nected from the junction of the twochokes to filament or ground, and theother from the 11 -plus end of the secondchoke to ground, will provide good re-sults. The chokes required for such usemay be of 1 or 2 millihenries inductance.The Hammarlund type (CH -X) are suit-able, are easy to wire, and inexpensive.

There are several factors which con-tribute to smooth and effective regen-eration. The antenna series condenseremployed in most short-wave receivershas a material influence because it de-termines the degree of antenna couplingand therefore the amount of energy ab-sorbed from the regenerative circuit bythe antenna. The voltages (plate andscreen) applied to the tube also influ-ence regeneration, as does the plate by.pass capacity.

Where "fringe howl" a terrific audiodisturbance which occurs as the tubegoes into or out of oscillation is ex-perienced, the condition may sometimesbe improved by the adjustments of theantenna or plate by-pass condensers. Amore likely remedy, however, is to shuntthe headphones or audio transformer pri-mary (whichever is connected in the de-tector plate circuit) with a fixed resistorof 100,000 ohms or higher.

For simple regenerative theantenna which will provide the best gen-eral results is the ordinary "L" type witha single lead-in wire. This antennashould be as high and long as practical,the lead-in should be kept clear of wallsor other objects, the insulation should begood, and the antenna and lead-in shouldhe one continuous length of wire with-out joints. If joints are necessary, theyshould be carefully soldered.

Special antenna systems have their ad-vantages in many cases-but for the mostpart are not entirely practical for usewith any type of receiver in which theantenna is capacity coupled direct to thegrid circuit of the first tube as is thecase in the great majority of regenerativereceivers.

POLICE ON SHORT WAVESThe elaborate short wave arrangement ofthe Police Department of New York City.

1936 SHORT WAVE MANUAL 7As explained on

page 3, bandspreading on shortwaves is a mosteffective feature.For this very im-portant work, Ham-marlund has pro-duced the famousband spread con-,densers, a model,Band ,Spread CondenserOf which is illus-

trated at the left. This model, known asthe MC -120B is used in the A.R.R.L."Ham" receiver described on page 26 ofthis manual. Its list price is 53.00.

The tank section, or the larger capac-ity division of this condenser, may beset and locked at any desired capacity.This permits the tuning section to spreadoarrow frequency ranges over the entiredial regardless of the range of the bandor the coils used.

Another important unit that Hammar-lund has developed for short wave work

-is the new Hammarlund variable coup-ling air -tuned intermediate frequencytransformer, shown here, below. Thesetransformers are designed to permitcontinuous variation of the mutual in-ductance between pri-mary and secondarythroughout a widerange of values with-out otherwise effect-ing circuit constants.The approximaterange of variation isfrom one-third criticalcoupling to over threetimes critical coup-ling. Both primaryand secondary a r ethoroughly i mpr e g-natcd 3 -pie Litz wind-ings having the ex-ceptionally high "Q"of 130 (power factorless than .000) Thetuning condensers are the familiar andpopular APC air dielectric type. Theimpregnated coils and low loss con-densers result in a highly stable unit re-gardless of conditions of temperature ofhumidity. Both tuning adjustments areon one side of the aluminum shieldwhich treasures 2" x 2" x 5" high. Threeof these units, known as the VT -465, arcused in the 3 -tube Pentode receiver de-scribed on page 22 of this manual. Theylist at $5.50 each.

The popular APC air -padding con-denser, which has so many importantshort wave applications is shown above.These ideal condensers maintain conslant capacity under any conditions oftemperature, humidity or vibration. One

VariableCoupling !PT

Air Padding Condenser

of their ingeniousfeatures is the size.For instance the 100mmf. units is only1.7/32" x 15/16" x1.1/2" high. Thebase is Isolantiteof course, and thecadmium platedbrass are solderedcarefully to properly spaced sol-

dered tie -bars. The sizes range from25 mmf. to 100 mmf., the list price ofthe smallest one known as the APC-25,being only $1.30 and the list price of thelargest, the APC140, being only $2.25.

Another important unit produced byHammarlund for the short wave receiveris the midget type EC condenser whichhas FO many uses. This is shown below.It is used for neutralizing, balancingand trimming. It is also excellent foradjusting multiple tune circuits or gangcondenser units. It may be attached di-rectly to the binding post of a socket ora condenser. The adjustment of the cen-ter screw provides a gradual capacitychange over a widerange. The dielec-tric is mica, andthe flexible plate isphosphor bronze.The base is bake-lite, 1-1/4"x11/16".The type EC -35,which has a rangeof from 3-35 mmf.lists at 40c.

A still tinier Hammarlund equalizingcondenser is the type "MEX." It is solight in weight that it is self-supportingin wiring. In this type the base is Isolan-tite and only 5/8 a 3/4". The dielectricis mica and the spring plate of phosphorbronze. This model is made only in onesize, having a range of_ from 3-30 mid.Its list price is 30c.

The Hammarlund aluminum tube shieldalso plays an important part in short wavereceivers. The complete isolation afforded '

by this shield permits the use of theenormous amplification possibilities orthe new tubes.

A special drawn -in neck completes theshielding between the control grid andthe plate. A removabig top is used to en-tirely shield the conwl grid cap. Thebody, cap adld base arc 'all made of heavyaluminum and designed for maximum

,cooling. HeasuresOr high by 1%"diameter, withstandard mountingcenter of 1-27/32".The shield isknown as the TS -50and lists at $.40

Mttl each.

Type EC

8 7 h HAMMARLUND

A BoyScout'sS. W.

ReceiverHIS set was described in

1 detail in "Radio News."This receiver was built byScout Robert Crockett ofPelham, New York, and is a good ex-ample of a design which aims at a happycombination of efficiency and economy.It is assembled on a wood base and panelto avoid the expense of a metal chassis.Also, the dials used, cost but a few centswhereas dials of the vernier or drumtypes would add considerably to the over-all cost. It will be noted, however, thatthe all important parts involved in thetuned circuits were selected with an eyefor efficiency, as typified by the Hammar-lund Isolantite insulated condensers.

The receiver employs relatively fewparts and is a simple one to construct-easily within the ability of the novicewho contemplates the construction of hisfirst short-wave receiver. Further, it isone which, when completed, will giveplenty of enjoyable reception. ScoutCrockett has succeeded in tuning in some300 short-wave stations with it.

No radical claims are made for the set

-such as loudspeaker operation, etc., butit will bring in the short-wave broadcast,amateur, pollee, aviation, television andcommercial 'phone and telegraph stationswith comfortable audibility. Europeanshort-wave broadcast stations are heardwith plenty of volume for clear head-phone reception.

One feature of this receiver which isout of the ordinary is the use of amidget air dielectric variable condenser(Cl) in series with the antenna circuit.It has been a common practice to em-ploy a "trimmer" condenser of the com-pression type for this purpose but,through the use of a variable air dielec-tric condenser here, readjustment isgreatly simplified inasmuch us a screwdriver is not required, and the variat'in capacity is far smoother than is thecase with the compression type con-denser.

There is frequently a distinct advan-tage in being able to adjust the antennaseries condenser readily. This con-denser varies the degree of antennacoupling. Now, if the antenna is closelycoupled to the detector circuit it tends toabsorb energy and thus prevent oscilla-tion, even when the regeneration controlis well advanced. On the other hand,close antenna coupling results in inureof the signal energy reaching the grid ofthe detector with correspondingly greatervolume at the headphones. Against thisis the fact that selectivity decreases asthe coupling is increased. Now then,


PANEL.SEE OCTout.)

194Str BOARD

COK.SOCKET.

TKISEwiS uROCR - -11REKSCBOKRO

t:ao p

C4

FC

CS

-SOCKET FOR30 TUBE

Fig. 1

the usual practice is to adjust theseries condenser (the coupling) so thatthe detector can be made to oscillatereadily throughout all ranges. The an-tenna absorption varies with frequency,however, so that when coupling is loos-ened to the degree required at frequen-cies where absorption is highest, it islikely to be found unnecessarily loose atother frequencies where antenna absorp-tion is less.

From this discussion it is seen that theadjustment of this condenser represent,a compromise in most receivers where apermanent adjustment is maintained.However, with the type of condenserused iii this "Scout" receiver, this can bereadjusted to meet the variations in ab-sorption at different frequencies. It can

also be adjuacd to provide loose coup-ling and therefore higher selectivity if in-terference is encountered, or to providecloser coupling when tuning in extremelyweak signals. In other words by varying this condenser as needed, the selec-tivity and sensitivity of the receiver areunder more complete control of theoperator and better reception is theresult.

The front panel of the receiver is of5/16 inch plywood with inch plywoodcleats screwed along the ends at the backfor greater rigidity. The baseboard is of

inch hard wood. The front panel isattached to the baseboard In nieans ofwood screws, or with wood plugs andglue; and is reinforced with two-inchtriangular wood corner brackets, gluedto panel and base at each end of thereceiver.

Before mounting the front panel onthe base it is well to drill the four holesrequired for mounting the panel controls,otherwise the drilling operation is likelyto impose a strain on the panel. Afterthe panel is drilled and is mounted onthe baseboard, then all of the parts canbe mounted in the positions indicated onthe picture wiring diagram, Figure L

The batteries required consist of twoNo. 6 dry cells for the filament supplyand one 45 volt battery of the type usedin portable receivers, or two 221/2 volt Cbatteries. Large size. B batteries are notrequired because the current drain ofthe single 30 tube is very small.

List of PartsIIAMMARLUND PRODUCTS

CI-Midget variable condenser, type MC.35-S

C2.M Wee* variable e undrnher. type M I.-110 -M

CS-Midget variable condenser, type MC -250.M

LI, L2, L3-Set of 6 -prong plug-in coils,type SWK-6

RFC-R.F. choke, type C11.8, 8 millihenriesMISCELL t NEOUS

24-Aeros us or Cornell-DubiUer condenser..0001 mfd.

C5Aerovos or Cornell-Dubiller condenser,.001 mfd.

R1-I.R.C. metaliaed resistor, 3 megohmsR2-liaxley 30 -ohm rheostatsW.--Cutler-Ilanamer, s.p.s.i. toggle switchI Type -30 triode vacuum tube

Eby 4 -prong socket, type 12 or Ham-marlund Code 8-4 Isolantite socket

1 Eby 6 -prong socket, type 12 or Ham-marlund Code S-6 Isolantite socket

8 Binding posts, suitably marked for con.necti one as shown in Figure 1.

to The HAMMARLUND

The

Dragnet( 2 Tube S. W. Set )

DESIGNED by the tech-nical staff of "Radio

News," this receiver was or-iginally described in thatpublication.

The "Dragnet" employs two of the lat-est types of 2 -volt tubes and is designedto take full advantage of their superiorfeatures. Although only 2 tubes are em-ployed, 3 -tube results are obtained be-cause the type -19 tube is a dual purposetype having two triode sections enclosedwithin one bulb. One of these triodes isused as a regenerative detector while theother provides one stage of audio -fre-quency amplification which aids materi-ally in building weak signals up to goodheadphone volume. The other tube, atype -34 variable -mu pentode, is used inan untuned stage of radio -frequency am-plification.

This r.f. stage serves a three -fold pur-pose. First, it provides an appreciableamount of r.f. amplification. It is aknown fact that for maximum amplifica-tion from tubes of this type they mustwork into a high impedance load. Theload which best satisfies this conditionis a tuned circuit. It is this type of cir-cuit, consisting of the coil Ll and con-denser C2 that is employed in the "Drag-net". Also, under actual measurementit was found that the common practice of

using a resistor input did not producenearly as good results as the choke, RFC,nor did chokes of lower inductance(millihenries) equal the one employed.

The second advantage of the r.f. stageis that it serves to completely isolate theantenna from the regenerative detectorcircuit and therefore eliminates absorp-tion of regenerative energy by the an-tenna, thus making regeneration muchmore constant and easier to regulate.

The third advantage is that with thisr.f. tube acting as a barrier, the r.f. en-ergy generated by feed -back in the de-tector tube when in an oscillating con-dition or when on the edge of oscillation,cannot be radiated and cause interfer-ence in neighboring receiver& In otbcrwords, this receiver is strictly a "non -blooper".

The parts used throughout were se-lected for their high efficiency, a featureof the greatest importance, especially inthe r.f. and detector circuits. Thus thecoil and tube sockets are of Isolantite,as arc also the forms upon which theplug-in- coils are wound, the insulation ofthe tuning condenser and the insulating

e.

att.-

CB

GN

v

CO

O

ra

vol 04

THL-X NUvdl4, GONG.XON TOP wg, Fv.rrroa vire4

5."- NG CEATINLX:45f

BOTTOM VIEW

Fig. 1

1936 SHORT WAVE MANUAL

COIL FORMVIEWED FROM

BOTTOM

L2 Ll

- .-[I

SECONDARY

TICKLER

Fig. 3

form of the r.f. choke. Even the antennaconnection terminal takes the form of atiny porcelain stand-off insulator to in-sure against losses. To reduce coil lossesto a minimum, the coil socket is mount-ed on bushings which elevate it approxi-mately 1 inch from the chassis. Half -inch bushings are supplied with eachHammarlund socket. Inasmuch as theyare not required for the socket of the-34 tube, two sets are used for mountingthe coil socket. The socket for the type-19 tube. is elevated on the bushings sup-plied with it.

The panel and chassis each consist of7 inch by 10 inch aluminum sheets.

The receiver are home.wound and the complete winding datawill be found herewith. The Hammac-lund Isolantite coil forms employed offernumerous advantages, in addition to thatof high efficiency. They are suppliedwith plenty of holes through which tocarry the ends of the windings to theprongs and therefore no drilling is re-quired. Also, they are equipped withknobs which have cardboard inserts,under transparent windows, on which thewavelength range of each of the coils maybe marked. The correct internal connec-tions to the four prongs of each coil arcshown in Figure 3.

In Fig. 1, the exact wiring is shown.

Fig. 2

Panel ViewCOIL DATA

Range Ll L2 Frequency WavelengthNo. 1- 6 6 18300.10710 15.8.28.0No. 2-10 7 13040- 6670 23-45No. 3-18 9 7140- 3850 42-78No. 4-30 12 4170- 2260 72-133No. 5-50 20 2380. 1220 126-245

No. 22 d.s.c. wire used for Ll,ranges 2, 3, 4 and 5; No. 28 d.s.c. forrange L

No. 28 d.s.c. for all ticklers (L2).Ll and L2 separated .14 inch, all

tan ges.Ll windings spaced to occupy 11/2

inches for coils 1, 2 and 3. Closewound for coils 4 and 5. All fieldersclose wound.

List of PartsIISMMARLI`ND PROM 4

C2-111idget variable condenser, type Xt1

140-MRFC-R.F. choke, type CH -82 Isolantite 4 -prong sockets, type 5.41 Isolantite 6 -prong socket, type S-65 Isolantite pIng-in toil forms, 4 -prong,

type CF. -4MISCELLANEOUS

CI, C7.-4;ornell-Dulsiller .00025 mfd.CS, C6-Cornell-Dubilier .0001 mfd.C4, C5, C9Cornel4Dubilier pigtail by-pass

condemners, .1 surd., 200 voltsale-Cornell-Dubilier pigtail by-pass con-

denser, .5 mfd., 200 volts111-1.R.C. metalised resistor, 5 megohms,

IA wattR2-Eleetrad potentiometer, 100,000 ohmsR3-1.R.C. metalised resistor, 100,000 ohms

45 wattR4-LR.C. metalized resistor, 1 megohn,

1/2 wattmetalised resistor, 1500 ohms,

% wattR6 -1.11.C. metalized resistor, 15,000 ohms,

MattR7-Taxley "Junior" rheostat, 10 ohmsSW-Toggle switch, d.p.s.t.1 Kura-Kasch vernier dial, 2% inches1 Midget porcelain stand-off insulator2 Insulated phone tip jacksI Binding post (for ground terminal)1 5 -wire battery cable, length optional1 Rubber grommet (for protecting battery

cable where it passes through cheris')2 11/2 inch bakelite knobs (for R2 and

R7)1 Aluminum panel, 10 inches by 7 inches.

and 1 aluminum chassis, 10 inches by5 Inches by 1 inch high

1.2 The HAMMARLUND

A Power Packfor

S. W.Receivers

TIlE power pack illustrated in the ac-companying photographs and dia-

grams was originally described in "RadioNews."

Many present day power packs proveentirely suitable for use with non -regen-erative receivers, or with receivers de-signed for the broadcast band only. Butwhen used with short-wave regenerativereceivers these units' hunt is so troublesome in many instances as to seriouslymar reception. This is particularly trueif the receiver is maintained in an oscil-lation condition for reception of c. w.signals.

Such trouble is usually traceable to theinclusion of nn inadequate filter in thepower' supply unit. It may be due toskimping on capacity, or to the use ofonly one choke, or perhaps 2 chokes liais-ing insufficient inductance.

Another common source of trouble isfound in unstable operation of the re-ceiver, particularly if it is one employ-ing a tuned r.f. stage ahead of the re-generative detector. Such instability isoften due directly to inadequate by-passcapacities across the various voltage tapsin the power pack.

Both of these types of troubles areeffectively eliminated in the unit de-scribed here. Two sizable chokes are in-cluded in the filter, and a total of 16 nail.for the filter capacity. in addition, acapacity of 4 mad. is provided acroi4each of the output voltage taps. Thehigh voltage to the filter is obtainedthrough a center -tapped resistor con-nected across the rectifier filament tofurther aid in hum reduction.

The filter circuit employed makes useof the choke input method. This ar-rangement has several distinct advan-tages over the capacity input type offilter. Most important is the better volt-age regulation obtained. This is espe-cially important in short-wave receiverswhich employ an r.f. stage and controlthe sensitivity by varying the cathode orgrid bias. Such control varies the platecurrent of the r.f. tube and as a result,unless good power supply regulation isobtained, the plate voltage applied to theother tubes will vary. This is one rea-son why in such receivers reducing thesensitivity of the r.f. stage may cause thedetector to spill over into an oscillatingstate.

Another common source of trouble isfound in unstable operation of the re-ceiver, particularly if it is one employ.ing a tuned r. f. stage ahead of the re-generative detector. Such instability isoften due directly to inadequate by-passcapacities across the various voltage tapsin the power pack.


t 1t

R2

A third, and perhaps sotnewhate left-handed advantage of this system is thatthe d.c. output voltage obtained withchoke input is considerably lower thanthat obtainable with capacity input. Thisis really an advantage because while fewshort-wave receivers employ more than200 volts on the plates it is difficult toobtain power transformers which willprovide such low voltage. The normaland least expensive power transformersprovide an a.c. voltage of 300.350 eachside of the center. When a condenserinput filter is used with these, at normaldrains, the d.c. voltage output is usuallyin excess of 300 volts-a value quite ex-cessive for most short-wave receiver,.Thus the use of the choke input permit,employment of the least expensive typeof standard power transformer.

The power pack described here pro-vides 220 volt., d.c. at a current drain of25 milliamperes. In addition it includesa 6 -volt filament winding rated at 1.5 am-peres whirl] will supply the filaments ofup to 5 tubes of the 6 -volt type. In theparticular model shown here the voltagedivider is provided with 3 adjustabletaps, thus supplying the high voltage andtwo intermediate values, all variable.

Another feature of thiswhich should not be overlooked is ther.f. filter consisting of the r.f. choke RFC,and the !a condenser C6 which has acapacity of 006 mfd. The purpose of thisfilter is to avoid the tunable hum some-times so troublesome in short-wave sets.

Now, the center taps of the high -voltage secondary and the 6 -volt filamentwinding of the transformer are groundedto the chassis at one of the mountingscrews of the input choke,

6V. 8+20 8f400 aMsoH li TO 100V. TO tam 10250X

t /SLACK TWISTED PAIR

I

tf411W-.

RFC I J

BOTTOMVIEW

SOCKET FOR -80RECTIFIER TUBE

5

1ITO

110 V.

Fig. 1

Fig. 2

This power pack should prove highlysatisfactory for use as a B supply unitfor any short-wave receiver which re-quires 90 volts or more on the plates. Ifthe, voltage required is less than thenormal output of the power pack it isobtained from the top tap of the divider,adjusting this tap to the exact value de-sired. If the receiver has heater type 6 -volt tubes their filament supply can betaken from the power pack also, afterfirst being sure that the filament wiringin the receiver is not connected to anyof the other wiring. Also, it will prob-ably be found desirable to rewire thefilaments with twisted pair if the fila-ment wiring was not originally of thistype.

The plate supply voltage obtainedfrom this power pack is almost absolutelyfree from hum. In tests made with a 3 -

tube tx.f. regenerative receiver not theslightest trace of hum could be heard,even when operating at 20 megacycles.

List of PartsC2-Aerovex. or Cornell electrolyticcondensers, 2-seetions, 8-8 mfd., 430volts, d.c.

C3, e4, CS-Acrolos or Cornell electrolyticcondenserts 3 -section, 4-4-4 mfd., 450volts, d.e.

(6--Aerovox mica condenser, .006 mfd.I:111, CH2wwThortlarson chokes, type T-

4402RIFC-lianonarlund type CH -X r.f. chokeIt I-Eleetrod 30 ohm renter -tapped Mo-

ment resistorI t 2 --.Elect rad 'Fru, olt voltage divider, type

C-200, 20,000 ohms, 50 watts, with 3adjustable intermediate taps

1 Eby 4 -prong tube socket, type 121 Eby 6 -prong tube socket, type 121 Eby 6 -prong cable plug, male

Sin -conductor ruble (of required lengthSW-Toggle switch, m.p.s.t.T-Thordareon power transformer, type F-

3472L Type -80 rectifier tube1 Six foot line cord with plug

Rubber grommet, % inch (for power cordhole In chassis)

Aluminum or steel chassis

14 The HAMMARLUND

The Radio Amateur's handbook

3 -TubeBand-

SpreadA C Set

0 0OUNER or later most ov)iters of re-generative receivers feel the urge to

try the use of radio -frequency amplifica-tion ahead of the regenerative detector.In the days when only triode tubes wereavailable the complications in this weresevere and at best very little amplifica-tion was obtained in the r.f. stage. Withthe introduction and popularization ofscreen -grid tubes and r.f. pentodes, how-ever, the picture has changed completelywith the result that a well designed r.f.stage adds tremendously to the sensitivityand general behavior of the regenerativereceiver.

The receiver illustrated here representsa good example of such a set. It is amodel constructed after the descriptionwhich appeared in "The Radio Amateur'sHandbook," tenth edition.

In the construction of this model therewas some variation from the original,mainly in the method of obtaining re-generation. The original had the ticklerin the cathode circuit and standard plug-in coils are not well suited to this ar-rangement. In the model described here,therefore, the circuit was changed to in-clude the tickler in the plate circuit. Nochange was made in the method of controlling regeneration-a potentiometer tovary the voltage applied to the screengrid.

Referring to the schematic circuit ofFigure 2, it will be seen that the r.f. stageis quite conventional in every respect. Ituses a -58 r.f. pentode, self biased.

The single audio stage is impedancecoupled to the detector circuit. It em-ploys a type -56 tube which is also selfhissed.

It is important that means for con -

TOP VIEW

TO TOPTTRIAINAL

OF VI,

TO COILSOCVCT N2.1

Fig. 1


I

trolling the gain of the r.f. stage be pro-vided on the front panel of such a re-ceiver as this. Otherwise even moder-ately strong signals will overload thedetector. If the regeneration controlalone were depended upon for this pur-pose the results would be highly un-satisfactory because in addition to de-tector overloading, there would be a dis-tinct loss of selectivity when regenera-tion is retarded to reduce the volume.On the other hand, by controlling thegain of the r.f. stage, the input to thedetector can be held down to a low level,full regeneration employed and thusmaximum selectivity obtained.

The band -spread system employed pro-vides continuous band -spreading bymeans of a small condenser shuntedacross the tank tuning condenser of eachstage. These tank condensers are con-trolled by individual knobs. These maybe seen as the two top control knobs inone of the accompanying photographs.The small band -spread condensers, how-ever, are ganged for control by the singlemain tuning control at the left end of thereceiver.

Not only does this system provide avery helpful degree of band spreading atany and all points throughout the rangeof the receiver, but it also provides singledial control within any band which hasbeen selected by means of the tank con-densers. Thus when the broadcast list-ener has tuned the tanks to resonance inthe 25 -meter broadcast band, for instance,he proceeds to tune in the individualstations in that band with the single maincontrol, much in the same manner as hewould tune in broadcast band stations ona modern broadcast receiver. The cir-cuits will be found to track fairly wellthroughout the full rotation of the bandspread dial, although some readjustmentof the r.f. tank condenser will be re-quired.

The model receiver shown here wasbuilt for use with Hammarlund standardplug-in coils and with the tuning capaci-ties used, will cover the short-wave rangefrom 19 to well over 200 meters, with ade-quate overlap, using 4 pairs of thesecoils.

The secret .of using a tuned r.f. stagesuccessfully, ahead of a regenerative de-tector, lies in providing thorough shield-ing. If shielding is inadequate there willhe interaction between the two circuitsto the extent that the tuning of one willreact on the other and regeneration willbe difficult to control.

This receiver is intended for operationfrom an a.c. power supply unit whichwill supply approximately 200 volts d.c.for the plates and 21/2 volts for theheaters. Should it be desired to employ

Fig. 2B batteries, the voltage divider consist-ing of R5 and B6 may be eliminatedand the "high" end of the potentinnieterbrought out to the 45 -volt tap on the Bbattery.

The chassis is made from a sheet of 16-

gauge aluminum, 17 inches by 11 inches.The edges are bent down 2 inches allaround, making the deck dimensions 13inches by 7 inches. The front panel is131/2 inches long by 7 inches high. Theshield cans each measure 7 inches long,444 inches wide and 43 inches high.

CI,

Gs.

List of PartsEIAMMARLUND PRODLCIS

C2-Midget variable condensers,MC20-S

C4-Midget variable condensers,MC -140-M

Ll, 1.2-Kit of 4 -prong plug-in roils,SV7K-4

1,4, LS-Kit of 6 -prong plug-in coil,type SWK-6

RFC--R.F. choke, type CH -X1 lsolantite socket, 4 -prong, type S-11 Isola:tilt° socket, 6 -prong, type S-62 Tube shields, type TS -502 Flexible couplings, type FC

MISCELLANEOUS

type

type

type

CS, C6, C8-..-Cornell-Dubilier .01 mfd., 200v.C7Cornell-Dubilier .1 mid., 400v.C9, C10 --Cornell DubiHer type SIC -2271.0 odd., 160v.C11, C12, C13-Cornell-Dubiller .00025

mid.C11--.Thordarsen audio choke, type 1-292711101.R.C. resistor, 5 otegidama112-I.R.C. resistor, 250 ohms, 1 watt113-hlectrad potentiometer, 10,000 ohm.

t-1.R.C. resistor, 50,000 ohms, 1 walld wire wound resistor, 15,000

ohms, S watts14(Eleetrarl wire wound resistor, 5000

ohms, 5 watts07-1.R.E. resistor, 100,000 ohmm, 1/2 wattH8-1.R.C. resistor, 5 megohms 1/4 wattR9-I.R.C. resistor, 2000 ohms, 1 watt1110-Yalley potentiometer, 50,000 ohms1 National illuminated drum dial, type H2 Eby laminated wafer sockets, 6 -prong1 Eby laminated wafer socket, S -prongI Eby strip, 5-0"....a IN.,. terminals)I Eby strip, 3 -gang (screw terminals)1 Eby strip, 2 -gang (tip jack terminals)I Aluminum chassis and 2 aluminum shield

cans (see text).All metalised txpe.

The HAMMARLUND 1936 SHORT WAVE MANUAL 17

Send for Catalog forCoin plete Information on

all HAMMARLUND products

gym, Biattou Tixidio-

ammarlundPREC/S/ONPRODUCTS

Manufactured by HAMMARLUND MANUFACTURING M.. Inc., 424-438 West 33rd Street, New York

All prices shown here arelist prices of parts used in

sets described in this manual.

HAMMARLUND Standard and MidgetIsolantite R. F. Chokes

T h e StandardChoke is particu-larly designed forshort wave, andultra short wovereceivers and trans-mitters but isequally effectivewithin broadcast hand. Compactness permitsmounting in isolated positions well removedfront stray RF fields. Four windings, moistureproofed, and carried on lsolantite spool. Pro-tected by radio frequency lacquer and cello-phane covering. Inductance -8 mh; DC resis-tance -70 ohms; distributed capacity -3 mmf;125 milliamperes. Choke is 1)4 x 34".Code :H8..........-$1.10

The Midget Choke is invaluable for use wherespace is at a premi ..... . Its tiny size, and light-ness permits it to he supported by its ownleads. Five universal wound pies mounted ona 31/1" Isolantite core, with roils impregnated toinsure ruggedness and minimize atmosphericeffects. Tinned copper wire leads, secured tolsolantite core with metal end caps. Length

across caps -11/4". Diam-eter - /2". Inductance -35 nth ; DC resistance-3 ohms; capacity 1 mmf.125 milliamperes.

Type ClIN CIIX

Type CH41

S JAI

HAMMARLUNDStar Midget Condensers

A very popular low

fllal,priced midget for setbuilders, experimentersand laboratories. There

rr

ks%' are types for receiving,

III I A\ wave tuning, re genera -and transmitting, for short

lion, antenna coupling,'OtiliT18" ' verniers, etc. Light in

Star Midges weight, strong and com-pact i n construction,

smooth as velvet in operation. Low minimumcapacity, low loss natural Bakelite insulation,non -corrosive aluminum plates. Easy single holemounting, .!4" shaft, 5/16" bushing, 1" bakeliteknob. Size 1.9/16" wide by 14/4" high. Depthbehind the panel from 11/16" to 1%2" depend-ing on rapacity. Available in sizes from 15innif. to 140 nunf.

Code SM-2S (2S mmf.) .5 .85Code SM-100 (100 must.). 1.00Code SM-140 (140 mmf.) - 1.25

New HAMMARLUND Low Loss CoilForms and Short Wave

Plug -in -CoilsThese attractively priced coil

forms are made of XP -53 die -electric, a remarkable new lossinsulating material. Rugged,durable and most important,extremely effective, for XP -53losses are extremely low. Itsanther color is natural . . . noartificial coloring to cause loss-es. The coil proportions providemost practical form factor. The

Type N" forms arc groove -ribbed for airspacing of windings. There are also flange grips.and neat meter index inserts, for wavelengthindications. Another clever feature of the formis a threaded shelf, molded inside, to permitthe mounting of a trimming or padding con-denser for tuning the coil to a fixed frequencyor for band spread arrangement.

Code SWF-1. (4 prong) S .35Code SWF-S (5 prong) .35Code SWF-6 (6 prong) ...

Hammarlund Short Wave Plug In Coils pro-ide maximum signal strength, and greatest se-

lectivity an all bands. Extensive laboratorywork results in practically perfect design ofprimary., secondary tickler, coupling and over-lap.

Wound on low loss XP -53 dielectric Ham-marlund plug in forms. Secondaries of the 17to 41 meter and 33 to 75 meter coils are ofheavy silver plated wire to reduce skin resist-ance losses to a minimum. The secondaries ofthe other coils are of silk covered copper wire.The 270 to 560 meter coil is of bank -wound litz.

SWK Sri of CoilsNo. 40 toll (wound roil, 4 prongs, 10.20 meters) $1.00No. 11 coil (wound roil, .1 prongs, 17-11 meters) 1.00No. 42 coil (wound coil, 4 prongs, 33-75 ) 1.00No. 43 coil (wound coil, 4 prongs, 66-150 meters) .75No. 11 roil I wound coil. 1 prongs, 135-270 meters) .75IICC-$ (wound roll, 4 prongs 250560 meters).- 1.25No 60 roll (wound roil, 6 prongs, 10-20 meters) 1.25\r.. (.1 roil wound coil. 6 prongs, 17-41 meters) 1.25N.,. 62 roil I ound roil, 6 prongs, 33-75 meters) 1.25No. 63 coil 1 wound coil, 6 prongs, 66-150 meters) 1.00No. 64 coil (wound coil, 6 prongs, 135.270 meters 1.00RCC-6 (wound roll, 6 prongs, 250-560 meters) 1.50SWK-4 ( four -prong roils 17-270 meters) 3.00SWK.6 I 0...prong coils 17-270 meters) 3.75

HAMMARLUNDIsolantite Coil Forms and SocketsThese roil forms are of

extruded Isolantite. Theirlow losses and effective sta-bility guarantees efficienthigh frequency results underall conditions.

Equipped with convenientblack enameled wooden han-dle with a flat top, in whichis a removable paper discfor writing in frequencies.A celluloid disc protects thepaper, a spring ring holdingthe disc in place. Surface is"non-skid," eliminating trou-bles encountered in windingon slippery surfaces. Thenumerous holes provided inthe form, make drilling un-necessary. The form is 11,,'2" in dismieter and21/2" long exclusive of knob and prongs. Madein 4, 5 and 6 prong types to tit standard sockets.

Code CF -4 (4 prong) ....... ..... 81.00

Code CF -5 (5 prong) 1.00

Code CF -6 (6 prong) 1.00

ElfType CE

Low loss sockets are justas important as low losscoils or condensers. Inthe Ha tttttt arlund Isolan-tite sockets, low loss iscombined with low cost.

Constant resistivity and perfect contact elimin-ates noise.

The sockets have glazed tops and sides. Theside gripping contacts are rust proof. They canbe used for sub -panel or base mounting. Madein four, five, six, seven and eight prong styles.They are all 214" long, and 13 wide, withstandard mounting centers of 1-27/32".

Code S-4 (4 prongs)Code S-5 (5 prong,.)Code S-6 (6 prongs)Code S-7 (large base, 7 prongs)Code 57-13 (small base, 7 prongs)Code 3w8 (8 prongs)

Acorn socket at right.Isolantite. For new highfrequency acorn tubes -954 to 955. 134" diameter.Five double grip silverplated phosphor bronzeprongs, eyeletted and lip-ped to base. Guaranteed perfect contact. Ha -alignment plug. Top, sides, and plug glazed.

Code S-900 . . $1.50

.60

.60

.60

.60

.60.75

Improved HAMMARLUNDMidget Condensers

The marked efficiencyof Hammarlund condens-ers at ultra high frequen-cies has been attained byextensive research in ma-terials and design, con-stant experimentationand careful workmanship,plus years of experience.

Isolantite insulation re-duces dielectric losses toa minimum, assuring1118X1111818 and uniformefficiency under all con-ditions of temperatureand humidity. Strictlynoise -free operation is in-sured with a new, splittype rear bearing, plusa new noiseless silverplated Beryllium wipingcontact. platednon - corrosive. solderedbrass plates eli ... inate vi -!oration. Shaft VI" in diameter, extending 5/16"beyond rear frame to facilitate ganging. Individ-ually tested for breakdown on 500 volts A.C.Available from 20 tumf. to (25 ona.

Code MC -140-M $2.50Code MC -100-M 2.25Code MC -35-S 1.50The Double Snared Midget, have wide

spacing, special bearings, and Isolantite, mak-ing them particularly suitable for ultra shortwave receivers and transmitters. Midline orsemi -circular plates in 20, 35 and 50 innif. sizes.

Type MC

HAMMARLUNDSplit Stator Midget Condensers

Like HammarlundSingle Midget Condens-ers, these duals incorpor-ate in their design everyrequirement of a highquality small size twogang condenser. Theirrigidity, low losses andcareful construction af-fords greatest electricaland mechanical efficiencyin all types of short wavereceivers, using two gang

tuning condensers. The entire condenser isbuilt on a strong Isolantite base, including ashield plate between the stators. Other specifi-cations arc the same as for the singles. Madefor single hole panel mounting. Overall lengthbehind the panel -VA.".

pool ttidgot

Double Spared

18 The HAM1VIARLUND

TheDoerle

Two -

TubeReceiver

MR. WALTER C. DOERLE is well-known for his various short-wave re-

ceiver designs and the receiver describedhere has been justly popular with short-wave. enthusiasts. Basically it is not un-usual in the circuit employed. However.careful consideration of design detailshas resulted in this particular Doerle re-ceiver being especially popular since itwas first described in the magazine"Radio."

Analysis of the detailed schematic cir-cuit diagram in Figure 2 shows the stand-ard tickler method of obtaining regenera-tion, and a capacity -coupled antenna cir-cuit. Band -spread tuning is provided bymeans of a small variable condenser, Cl,shunted across the larger tuning capacity,C2.

The condenser C2 is used for tuningto the desired range, then the smaller

condenser will spread the stations in thisrange over a wide area on the main tun-ing dial. Inasmuch as the smaller con-denser is utilized for all exact tuning, itis controlled by the large dial in thecenter. The "rough tuning" condenser,C2 requires less critical adjustment, andmay therefore be controlled by a smallknob, as shown at the lower right cornerof the front panel. Some builders preferto have the large condenser controlled bythe main dial and to use the smallercondenser more in the nature of a trim-mer. Where this system is preferred itis only necessary to transpose the posi-tions of the 2 condensers on the panel,the wiring of the receiver remaining thesame as shown in the picture wiring dia-gram.

Regeneration is controlled by meansof the potentiometer, R2, A .25 mfd.

PHONES13+4S TO 90V 9- A+ A-

TOP VIEW --2yoPlv

8+45 TO 90V.. 8- A+ A.- 2 °R 3 V'RfCPHONES.

SW

BOTTOM VIEW

Fig. I


Fig. 2

by-pass condenser, C5, is connected acrossthis potentiometer to ground-its pur-pose being partly to by-pass any noisethat may develop in the potentiometer.The condenser C4 is the normal plateby-pass condenser completing the r.f.plate circuit to ground, thus by-passingthe primary of the audio frequencytransformer.

A type -30 tube is employed for theregenerative detector and another for thesingle audio stage. Two 11/2 volt drycells are used for the filament supplyand arc controlled by a rheostat whichis mounted back on the chassis, as itrequires only occasional adjustment.

Hammarlund plug-in coils of the 4 -prong, 2 -circuit type are used.

The chassis consists of a piece of 16 -gauge aluminum, 131/2 inches long by 11inches wide with the four corners cutout and the four sides bent down toform walls 2 inches high, leaving a deckspace 91/2 inches long by 7 inches deep.The front panel, also of 16 -gauge alu-minum, is 10 inches long by 7 incheshigh.

It will be noted in Figure 1 and inthe photograph that there are five ter-minals shown on the battery terminalstrip. Only four of these are used anda 4 -gang strip will therefore be satisfac-tory.

To tune, first find proper adjustmentfor the antenna condenser, C-6, by ad-vancing the regeneration control untilthe circuit breaks into oscillation, thentuning throughout the range with con-denser C2. If it cannot be made tooscillate throughout this range, decreasethe capacity of the condenser, C6, untilit is found possible to maintain oscilla-tion throughout the entire tuning range.lf, on the other hand, too much regen-eration is obtained, then increase thecapacity of C6.

Panel View

Once the proper control of regenera-tion has been obtained, the tuning andoperation of this receiver will he foundextremely simple. The condenser Cl willaid materially in tuning in all the sta-tions to exact resonance, or in spreadingthe stations out on the dial, when tuningin, on the more congested bands.

The antenna for this receiver shouldbe a comparatively short one, about 50feet, exclusive of course, of the lead in.

For increased amplification for loudspeaker reproduction, an additional stageof audio amplification can be added, us-ing the same circuit principle, indicatedin Figs. 1 and 2. Use however, a sep-arate chassis for this stage, since crowd-ing of this additional material on thechassis, will mar the effectiveness of thereceiver.

List of PartsHAMMARILLND PRODUCTS

C1-Midget variable condenser, type Mt. -35 -9

C2-Midget variable condenser, type MI140-M

C6 --Equalizer condenser, type EC -35RFC -11.F. choke, type CH -X1 Set of 4 prong plug-in soils, type SWK-41 4 -prong loolantite socket type S-1

MISCELLANEOUS3, C4-Cornell Dubilier mica condenser

.00025 mfd.CS-Cornell Dubilier pigtail by -pas con.

denser, .23 mfd.R1-1.R.C. resistor, 1-5 megohmsR2-El d, type 111-205 potentiometer,

30,000 ohmsR3-Eleetrad, type R1.204, 10 ohm. rheo-

statSW-Toggle switch, s.p.s.t.T-Thordorson type T5736 a.f. trans-

former2 Eby 4 -prong eorkets, wafer type, or Ham-

marlund Code S-4 Not/Intim sockets1 Kurs-Ktsch vernier dial (large)1 Aluminum Howie panel and chassis1 Eby 2 -gang terminal strip (tip jack ter-

minals)1 Eby 2 -gang terminal strip (screw ter -

minas1 Eby 4 -gang terminal strip (screw ter-

minals

.)0 TI, HAMMARLUND

The "Skyscraper"3 -TubeT. R. F.

SetAn effective short-wave receiverequally well adap-ted to broadcast oramateur service.

VOLUME

LH

"r HIS three tube tuned r.f. ret eiver or -I iginally appeared in Radio News-

the second of the Radio News laboratoryreceivers. Following are some of its un-usual features:1. Continuous band spreading.2. Extreme sensitivity.3. Two tuned circuits for selectivity.4. Battery or power pack operation.5. Flexible control of sensitivity and

olume.6. Complete freedom from r.f.-detecior

interlocking.7. Single dial band -spread tuning.H. Most favorable L/C ratios for all im-

portant bands.9. Covers from 15 meters to 560 meters

continuously.10. Ample output for loudspeaker opera-

tion. Outputs for headphones, mag-netic speakers or dynamic speakers.

11. No body capacity.

12. Complete freedom from hum whena.c. operated.

The advantages of a really good stageof r.f. amplifies ' , ahead of a regenerative detector are not fully appre-ciated by the average shortwave con-structor, as indicated previously. Theoutstanding ability of the several avail-able commercial receivers is widely rec-ognized but as a rule the home construct-or has not been very successful in apply-ing r.f. tubes in regenerative receiver cir-cuits. The outstanding reason for thisfailure has been the lack of proper shield.ing and filtering, and a contributingcanoe has been the use of coils of unsuit-able design.

Regeneration control is made muchmore consistent and stable, due to thepresence of the r.f. tube which acts as abuffer ahead of the regenerative circuitand thus prevent, antenna absorption.

Fig. 1


Thus several distinct advantages aregained through the use of the r.f. stage.

After several weeks of testing on ac-tual reception of short-wave signals the"Skyscraper" worked out retnarkabl3well and in sonic respects een exceededexpectations. In the matter of r.f. gain,for instance, it was found that many sig-nals which ordinarily would be consid-ered only moderately strong, werebrought up to such a level in the r.f.stage (when the sensitivity control wasturned on full) as to overload the detec-tor. Other signals which were weak on anordinary regenerative receiver, were re-produced by the "Skyscraper" with morethan adequate loudspeaker volume. TheEuropean and South .American short-wave broadcast stations, for instance,were many t. -s tuned in with far inurethan normal room volume. "Hari" sta-tions were good on all bands. Perhapsthe most outstanding of all was the re-ception in the 20 -meter "ham" hand.

The. excellent operating characteristicsof the "Skyscraper" art- accounted for toa considerable extent by the coils em-ployed. These are the new HumourLundplug-in coils in which XP -53, a newly de-veloped dielectric, is employed for th.-forms. This new material rates amongthe best yet, is sufficiently inexpensive topermit the coils and forms to he mar-keted at ordinary prices.

The Hanimarlund coils are tuned by aband -spreading condenser arrangement.The tuning condensers CI and C2 are of20 mmfd. capacity and are ganged to-gether to the drum dial. The band settinecondensers, C3 and C4 are of 140 =dd.each and are controlled by individualdials.

The special "Skyscraper" chassis is12;8" long, r wide and 3,4" deep.

The small panel on which the drumdial is mounted is 95A inches high by 3inches wide. This panel is mounted di-rectly on the front of the chassis.

.....sp. ..''V ' 11.\ -

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1

cv won. ra. 44 nor

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CO ...T' ,,O jS P'

Ca

Stil.V. Ili,ON"... 1411Y..irreNV.a at..41r41 _p. 1111P417.,410llMli

oi.

p .,

I'..7 .

R

The two box shields arc each 4V2 incheslong and 6 inches high.

List of I'artsHAMM ARLUND PROM iCTS

Cl, C2-.Midget variable condensers, typeMC20-S

C3, C4.-Midget variable condensers, typeMC -1.14)M

CS-Midget variable rontlentters, type MC -35 -S

C6-Paildine. condenser, type MICS.701.1-Standard set 4 -prong plug -In roils,

Type 1041%-61.2-Standard .et &prong plug-in roan,

type SW14..6IliECIRE choke, type CH -8REC2ws111, choke, type CH -XI I.olantite euelet, 1 -prong, type S-1

1.olantite sockets, 0 -prong, type 5-62 rube shields. type TS -501 Flexible coupling, type FC

MISCELLANEOUS PARTS

C7, C8, C9.-wAeroux or Cortical .0001 mfd.C10.--.-Aerovox or Cornell .01 turd., 400v.CI I-Arroyos. or Cornell ran type con-

denser, 1 mfd., 200v.C12-Aerovoit or Cornell electrolytic con-

denser 10 mfd., 25v.C13. C14, 4:15-terovits or Cornell con-

densers, .01 mid.nl-Elertrad potentiometer, 25,000 ohms112-Electrad potentiometer, 50,00(1 ohm.R3-Eleetrarl potentiometer, 500,000 ohm.R4-Eleetrad voltage divider, 50,000 ohm,.

25 walla.C. re.i.tor, 100,000 ohms, 4!, watt

116-1.R.C. resistor, 250 ohms, .1,4 wattR7 -1.11.C. reeistor, .4 megohm08-1.41.C. resistive, .5 megohmR9-Electrad resistor, 700 ohm*. 10 wattsCII-Thordarson AF choke, type T-2927T-Thordarson nnrymt transformer, type

T-6806SW-Toggle switch, ilpst.1-Eby wafer ....Picket, 0 -prong1-Eby 4 -hole cable plug, female1-Eby Alessi, mounting four prong cable,

male1--.4.1.iy twin lark speaker -trip1-Ebv 3 -sang binding post stripls-Eby twin lack speaker strip1-National Drum Dial, type1-Panel and Chassis2-Solid shaft couplings1 -4 -wire. 3' cable2-Kura-Kasch vernier dials1..-.3" length, 1/4" diameter bakelite rod1-Shleld can 2" diameter

22 The HAMMARLUND

A3 -TubeS. W.

PentodeReceiver

THIS 3 -tube Super was originally described by M. Harvey Gernsback in

Short Wave Craft.A 6A7 is used as the first detector and

oscillator, a 6F7 as the first I.F. amplifierand audio amplifier, and a 6B7 as a se-cond I.F. amplifier, second detector, anddelayed AVC tube-three tubes perform-ing seven functions. The 617 is a penta-grid grid converter, the 6F7-a combin-ation variable mu RF pentode with aseparate triode, both sections of the tubeemploying a common cathode. The 6B7consists of a variable mu RF pentode andtwu separate diodes.

This is not a "freak" receiver requir-ing delicate manipulation of many con-trols. There are only three controls,-avolume, main tuning, and antenna trim-mer.

The first detector and oscillator coils

arc the standard Hainmarlund XP -53, 4 -prong plug-in type.

The new Hanunarlund "variable coup-ling" air tuned I.F. transformers areused, affording a tremendous high gainas well as a high fidelity output. Two ofthe I.F. transformers used have to haveslight changes made in them for use inthis receiver. In one ease, it is necessaryto remove the control grid lead, so thatit appears at the bottom, and in the otherunit the control grid lead has to bebrought out at the opposite end to whichit now goes. This is done in the followingway. To change the position of the gridlead, first take off the collar from thetop of the plunger rod which is held inplace by one set screw. Then take outthe four screws-there is one on eachside of the adjustment screws on topand bottom. Now slowly and carefullyremove the coil, being sure to see that

Al A2

ca:

r l UN

.02

juidIECIS

C2

L2

L2 br---1

F

6A7DE7.- OSC.

A

FM."'

8 55

6F7461.F.AWNO

RI RII

CIS

512

6137235LF.-2S110E7:

- fe1213'

R14C21

R18

I.F.T.3

it6.3 V., A.C.- D.C. El+ 250 V

CMR 15

B -, CND. CONNECT TO CHASSIS

-a;517

C i8

ES

Vy

O

RS

Fig. 1


4111111 44-

_E.1"-e3 E2 RI 11.11nil c

LICOIL-

SOCKET 0 -

c., e L2COILCI .11 v..P SOU:e

cam ig)0I.F. T.1

CAP fbc.° 6A7

I.FT. 3

GRID VP GPO

:4

s so LE7:2

6 bF7

[AP 6137

........--' ,,%e.

.

PHONES

TO ANTENNA 6.3V. /3- 84-A.C.-D.C. GND 2505.

Fig. 2

the spring on the plunger does not popout. Now take the grid lead off the topcoil lug and solder on a lead of theproper length to reach your tube cap.Then drill a hole in the opposite side ofthe can and insert this new grid leadthrough this hole, while, of course, plac-ing the coil back again in its originalposition. Now with the other coil, thesame removal procedure is followed ex-cept that the grid lead is not taken outfrom the side of the can. It is left at thebottom. This is done since the seconddetector is a diode and the diode con-nection must be made to the base of thetube and not to the cap. Be sure that allcontrol grid leads are covered with metalshielding braid, at leaSt to within 'A'of the point to where the wire is sol-dered. For complete satisfaction, theseI.F. transformers should be lined upvery carefully. This is done by using an0.25 milliammeter in the following way:Connect the set up and plug in the set ofcoils covering the 49 meter band. Inci-dentally, it is a good plan to remove aboutone and a half turns from the grid wind-ing of the oscillator coil on this particu-lar band to insure proper tracking. Nowturn the dial until a signal is picked up,bringing it up to a maximum with the aidof the antenna trimmer. Connect the mil-liameter in series with the B plus leadto the receiver. With 250 volts appliedto the set, the meter should read between20 and 25 mills. Adjust the set screwson the sides of the can of the first I.F.Do this slowly with a wooden or Bake-lite screw driver, and note the meterreading. Adjust the other LF.'s similarly.Now detune the set slightly with themain tuning control. The meter readingshould go up as the set is tuned awayfrom the station. Now tune the stationin again and repeat the lining up pro-cedure of the I. F. transformers. Watchthe meter reading and adjust the set

Panel Viewscrews for minimum current on themeter. If the station is fading, the meterwill fluctuate continually during the op-eration, and it will be necessary to takean average reading on the meter. Repeatthis procedure once more for certainty.

Be sure, that the shield separating thevariable condenser sections is grounded.

The plungers on the I.F. transformersshould all be set in about the same po-sition for selectivity control.

List of PartsHAMMARLUND PRODUCTS

Cl, C2-...Split stator midget variable eon.denser, type MCD.140-M

CS-Midget variable condensei, type MC -5041

IFTI, 1FT2, 1FT3-VT-465 transformersLI, L2-Standard 4 -prong plug -in -coil kits,

type SWIL.4I Isolantite small base 7 -prong socket, type

S -7B2 Isolantite sockets, S -prong, type S -S3 Tube shields, type TS -50

MISCELLANEOUS PARTS

RI-Electrad potentiometer, 100.000 ohm-112-I.R.C. resistor, 50,000 ohms, 1/2 watt113, R12, R19-I.R.C. resistors, 100,000

ohms, 1/2 wattR4-I.R.C. resistor, 300 ohms, 1 wattR5-I.R.C. resistor, 20,000 ohms, I wattR6, R11, R17-I.R.C. resistors, 10,000

ohms, 1/2 wattRI, RIS, R18-I.R.C. resistors, 1,000,000

ohms. 1/4 watt118-1.11.C. resistor, 100,000 ohms, 1 watt119-I.R.C. resistor, SOO ohms, 1 wattR10, R16-I.R.C. resistor 500,000 ohms,

1/2 wait813--4.R.C. resistor 400 ohms, 1 wattR14-I.R.C. resistor 1500 ohms, 1 wattC5 --Cornell condenser, .00025 mfd.C6, C7. CIS, CO, CUL C12, C13, C14. C15,

C18, 1:20 --Cornell condensers .1 mfd.,500 v.

C22-Cornell condenser, .01 mfd., 500 v.C11, C24-Cornell condensers, .5 mfd.,

500 v.C16-Cornell condenser, 1 mfd., 500 v.C19-Cornell electroyltio condenser, 5 mfd..

25 v.C4, C17, C21-.001 sold. condenserC23-Cornell condenser, .001 mfd.2 Eby 7 -prong small wafer sockets1 Eby head phone terminal strip1 Eby antenna- g d terminal strip1 Eby ground binding post1 Vernier tuning dial1 Front panel, 111/2" z 7"1 Chassis 81/2" r 111/2'

24 The HAMMARLUND

An AC -DC2 -TubeS. W.

ReceiverTHIS unusual high frequency univers-

ally powered receiver was originallydescribed in the "New York Sun" byLouis Martin.

Though hut two tubes are used, thislittle receiver has an untuned R -F stage,a tuned regenerative detector and audioamplifier, and a rectifier. It is perfectlystable, oscillates easily from 200 to 15meters, and provides foreign receptionwith surprising ease. In fact, during atest, four foreign stations were tuned inquite easily and heard on a 5 inch dy-namic speaker. The amount of hum whenused on AC is negligible while the re-ceiver is regenerating.

As you will note from the circuit, Figs.1 and 2, the first tube is a 6F7 and thesecond is a 12A5. The 6F7 is really twotubes in a single envelope; a pentode anda triode. The pentode section is con-nected to the antenna by way of the RFchoke CH -1. The output is then con -netted to the triode section through theuse of the RF coils, as shown. The pen-tode section of the 6F7 is not tuned.

The 12A7 is a combination pentodeamplifier and power rectifier of the halfwave type. This tube was designed foruse in "Cigar Box" receivers, and issuited admirably for our purpose here.The secondary of the audio transformers

Panel View

is connected to the grid and C -bias re-sistor of the pentode amplifier, and theaudio output is fed to the phones ormagnetic loud speaker.

Rectification of the power voltage isaccomplished by the diode section of the12A7, which is equipped with a separatecathode for this purpose. The base -pinconnections of the two tubes used in thisreceiver are shown in Fig. 3.

It is important that the filaments of thetubes and the connections to the rectifierhe made exactly as shown. The terminalsof the power plug have been labeled plusand minus and these wires must be tracedcarefully when wiring the receiver. The6F7 heater must be in that side of theline labeled "negative," else there is apossibility of cathode - heater leakagedeveloping rapidly and ruining the tubes.The resistor should be placed whereventilation is best, for this resistor dis-sipates considerable heat which can befelt quite a distance away. Do not bealarmed if your hand should get com-fortably warmed 12" or 18" away fromthis resistor.

Condenser C3A is shunted across C3,the main tuning unit, and is a bandspread condenser. On 50 meters, half arotation of this condenser correspondsto 1/20th of a rotation of the main tuningcondenser, so that the band spreading isvery good on this crowded channel.

The sockets for the tubes and the tun-ing coil are of the type which are raisedabove the board. This mode of construe-


INIONES OR MAGNETICSPEAKER

110vA-L.le D.C.

Fig. 1

lion is quite essential in bread -board re-ceivers which utilize complicated wiringto a given socket.

Of course hum may be apparent whenused on AC unless care, painstaking care,is taken to keep all AC leads away fromthe tuning condenser, coil, and grid leakand condenser.

If the receiver is to be constructedfrom parts lying around the house, thenthe audio transformer may be replacedwith resistance coupling. The plate re-sistance should have a value of 50,000ohms, and the grid leak a value of onemcgohm. The coupling condenser shouldhe about .006 to .1 mfd.

Fig. 3

List of Parts11151MAH1.1 ND PRODUCTS

CS-Midget variable condenser, type MC -1 40 -M

C3A-Midget variable condenser, type MC -35 -S

CHI, CH2-RF Chokes, type Ell -X1 Isolantlie socket, 6 -prong for roll, type

S.62 Isolantite sockets, 7 -prong, type S-78I Kit of 6 -prong plug.in coils, type SWK.6

MISCELL 'S I s PA.WEN

Ll-Cornell-Duhilier condenser, .1 add.C2Cornett-Dubilier condenser, .0001 tad.CA--Cornell-Dubiller condenser, .0005 mid.C.5Cornell-Dubilier electrolytic, 25 nifd"

25 v.I:6, eleetrolytics, 8

mid., 200 v.C3-Cornell-Dobilier condenser, .02 =fel.R1-1.R.C. resistor, 300 ohmsH2-1.R.C. grid leak, 3 megohmsR3-Eleetrad tapered potentiometer with

line switch. 7500 ohmsR4-Electrad resistor, 1000 ohms145-1-Seetred resistor, 300 ohms, 30.50

wattsEl-Audio transformerCH3--Small 400 ohm AC -DC filtered chokeI Eby antenna -ground binding post1 Eby speaker binding poet1 7 a 10 aluminum panelI 10 a 11 wooden baseboard

54111.DED COO

CHI

V4D co

CI

r7C2

R2

C3

C3A

6F7 12A1NEATER REAM

VOLUut meACGITIERATIONcoma.

R3 . T

CH2

(

:s7

sr

RS

GANGED TO R3

NO V.A.C.O.0

OCS

P$PICS OR PANNIMC 1101.AKLR

Fig. '2

The HAMMARLUND

The

A.R.R.L.

"Ham

ReceiverTHE

receiver described here is onewhich is featured by the American

Radio Relay League and the magazineOST as an ideal job for a budding"ham". This receiver was described indetail in the A.R.R.L. booklet "How toBecome a Radio Amateur," 3rd edition.

To quote from the descriptive articlein this book: "The receiving set we de-scribe is of simple design and construc-tion. It is easy and straight -forward to as-semble and operate, and yet will readilybring in amateur signals from distantstations with a suitable antenna andground.

13+45 5+ C -4t5 A+ A -3V "T.tO 135V 45V. TO 13.5V. 3V. B -C+

Fig.

"Some of our readers may notice thatthe circuit is similar to the old familiar`three -circuit' tuner so commonly builtby broadcast listeners in the early daysof broadcasting. Do not think, for thisreason, that it is not a particularly goodamateur receiver. It may surprise youto know that this tuner, with occasionalmodifications, is used in the majority ofthe aniati ur stations in this country.Much of the international amateur work,expedition communication, etc., is donewith receivers using this circuit."

While this little set was designed pri-marily for the reception of C. W. and'phone signals from "ham" transmitters.the very features which make it a good"ham" receiver will make it a good re-ceiver for any type of short-wave work.

The tuning condenser really consistsof two condensers assembled in a singleframe. The 100 mmfd. section is used forcoarse tuning or band setting. Thesmaller sections provides a capacity of 20mmfd. and it is with this portion that thefine tuning and band spreading is ac-complished. Its shaft is brought throughthe front panel to the main tuning con-trol. The knob for adjusting the largersection is at the rear of the condenser,behind the panel. The band spreadingpermitted by this arrangement is an in-valuable feature of the receiver whenoperated on the 20, 40, 80 or 160 -meter"ham" bands and is a decidedly usefulfeature on other ranges as well becauseit spreads the station out on the dial sothat instead of two or three stations fall-ing within one degree, as they do on somany receivers which do not include thisfeature, they are spread out over a dialrange of perhaps five or ten degrees andthus tuning is much simplified.

Regeneration in the detector circuit is


Fig. 2

accomplished by means of the usualtickler and is controlled by means of thevariable bypass condenser, C2.

An aluminum front panel is used tominimize body capacity while tuning thereceiver. This panel is screwed to thefront edge of the wood baseboard. Thethree Hammarlund Isolantite sockets-this type of socket is recommended be-cause of their low r.f. losses --are elevatedapproximately Y8 inch above the base-board by means of bushings which aresupplied with them. Similar bushingsprovide a convenient means for mount-ing the 3 terminal strips.

The receiver as described here pro-vides excellent results when Hammar-lund standard 6 -prong plug-in coils areused. However, some constructors mayprefer to wind their own coils and thenecessary data are therefore given herebased on the use of Hammarlund hawtile coil forms.

Coil DataLI L2 L3 Frequency Range

No. 1 70 20 10 1000 to 2200 kc.No. 2 30 10 10 2250 to 4200 kc.No. 3 11 7 5 4200 to 9000 kc.No. 4 5 5 5 9000 to 18000 kc.

All coils are wound in the same direc-tion using No. 30 double silk -coveredwire, close wound. Approximately 1/16inch spacing is provided between coils.In each case the grid coil (L1) is thetop winding, the tickler (L2) is in themiddle and the antenna coil (L3) at thebottom. The top end of die grid wind-ing corresponds with the coil terminalmarked No. 1 on the schematic diagram,the lower end to No. 6; the top end ofthe tickler to No. 3; the lower end of thetickler to No. 2; the top end of theantenna coil to No. 4 and the bottom endof the antenna coil to No. 5. The num-bers marked on the coil socket in thepicture wiring diagram, Figure 1 corre-spond to the coil terminal numbers onthe schematic diagram, Figure 2, and the

a

Panel View

ends of the three windings should connectwith the coil form prongs indicated bythe numbers on the coil socket.

The tubes used are the popular twovolt type. A rheostat of 10 ohms resist-ance is used to control the three voltsupply necessary for these tubes. For thispurpose a pair of 11/2 volt standard drycells may be used. The -30 tube is usedas the detector and the -33 pentode out-put tube is in the single audio amplifi-cation stage.

A metal chassis may be used. Be sure,though, to see that all leads are properlyinsulated, and that all grounds are madedirectly. Follow too the many layout sug-gestions, provided within the descriptionsof the other receivers shown in thismanual.

List of PartsIt.4MM.4RLUND PRODUCTS

1.1-Midget variable condenser, type MC -120D, 2 sections-one 100 mmfd.and one 20 nimfd.

C.2-Midget variable condenser, type MC -140 -M

C4--Equallser condenser, type E1 -551.1. L2 L3-Standard 3scireult, 6 -prong,

plug-in coil kit, type SWK-6, or four6 -prong roil forms, type CF -6

RFC -15.F. choke, type C11 -X1 4 -prong Isolantite socket, type S4I 5 -prong Isolentite socket, type S-5I 6 -prong Isolantite socket, type 5-6 (for

toil)MISCELLANEOUS

C3-1:ornell-DubIller condenser, .0001 road.Ill-Elect...id type R1.204 rheostat, 10 ohmsR2 -1.R.1:. metalised resistor, 2 megohmsT-Thordarson type It -260 audio trans-

formerI Eby 2 -gang strip (Op Jack terminals)I Eby 2 -gang strip (screw terminals)1 Eby 5 -gang strip (screw terminals)1 Kura -Kitsch vernier dial (small)1 7 inch by 10 inch aluminum panel. 16 -

gauge1 Wood baseboard, 91/2" inches by 7 inches

bya inh thick.1 loggia switch. s.p.a.t.

28 7'he HAMMARLUND

The GainerTHE model of the "Gainer" shown here

is an adaptation of the original re-ceiver developed by the technical staffof "Radio" and described in that maga-zine. The detector is one of the new606 tubes and is the equivalent of the-57 except that it is intended for opera-tion from a 6 -volt battery or transformer.The type -76 tube employed in the audiostage is the 6 -volt equivalent of the -56.Either a storage battery or a 6 -volt a.c.filament supply may be used. For theplate supply either a R eliminator or Bbatteries may be used. The voltage maybe up to 200, although 135 volts will do.

Band -spreading tuning is provided, the

List of fartsHAMMARLUND PRODUCTS

CIe-Midgetvariableconcientler,type31C.20-S

C2-Midget variable condenser, type MC140-M

C3-Equaliser condenser, type EC -35LI, L2-Four.prong plug-in coil set, type

SWK-4RFC-R.F. choke, type CH.X1 Isolantite 4 -prong socket, type 5-1 ((or

sellMISCELLANEOUS

C4-eAerovoz mien condenser, .00025 mill.C5.-Aerov on mica condenser, .01 mfd.C6-Cornell-Dubilier .1 mfd., 200 voltsC7Cornell-Dubiller .5 odd.. 200 voltsCB-Aertivon pigtail mien condenser, .00015

mfd.11:11.-wThordarson 200 henry audio chokeR1-I.R.C. resistor, 1 to 5 megohms112-YarJey potentiometer, 50,000 ohmsR3-1'axley potentiometer, 500,000 ohms114-I.R.C. resistor, 10,000 ohms, 2 watts1 Eby 5 -prong socket, type 12, or Ilam-

marlund Code S-5 Isolantite socket1 Ehy 6.prong socket, type 12, or Ham-

- Code S-6 Isolantite socket1 Eby 5 -gang strip (screw terminals)1 Eby 2 -gang strip (screw terminals)1 Eby 2 -gang strip ( tip jack terminals)1 Kure-Kaseh vernier dial (large)1 Toggle switch d.p.s.t.I Aluminum panel. 12' a 7'1 Baseboard, 101/2" long, 914" deep

140 inuild. condenser, C2, serving as thecoarse tuning or band -setting condenser,while the critical tuning is accomplishedwith the 20 mmfd. condenser, Cl, whichis controlled by the main tuning dial.

The coils employed are the standardHammarlund plug-in coils of the 4 -prong413e-

A-6IC

MSV.

a -

as455.61135-70250V.

R3

REAR VIEW OF PANEL

CI

TO TOPTERMI'AL

OF V

RI

110 elle"11 sr'

O

RR VI

ca OILC50CACT

C5 6D6

TOP MEW Of BAXECARD

AMC

15O


The ArgonautMI MS 2 -tube. dry -cell operated receiver/ was described in "Short Wave Craft."The antenna series condenser, C3, as

shown in Figures 1 and 2, is quite novel

Fig. I

in its construction. instead of using theusual equalizer type, adjustable con-denser here the designer made his owncondenser by winding 14 turns of insu-lated hook-up wire tightly around a 1%inch length of bus bar, the hook-up wireand the bus bar each forming one plateof the condenser. The capacity of this:condenser is varied either by slippingthe coil partly off the bus bar, or byunwinding turns. The sole advantageoffered by this kink is the fact that itcosts nothing. Actually it is cumbersometo adjust and it is suggested that the con-structor will save time and trouble bysubstituting a Hammarlund type EC -35equalizer condenser here, its cost bringonly a few cents and easily justified bythe greater convenience and permanencyof adjustment.

,4111111 Aggilet&

5- A+ A- ANT. ANT GNO.

TOP VIEW 2v.

Fig. 2

List of PartsHAMMARLUND PRODUCTS

1:1-Variable condenser. type MIC-140-11choke, type CH -X

2 Isulantite sockets, 4 prong, type S. t1.-Set of 1 -prong 2 -circuit plug-in coils,

type SWK-4Si I SCEMANEOUS

C2-Cornell.Dubilier condenser. .0001 mfd.C3 ---See text

condenser, .00025 mfd.C5--CornellDubiller condenser, .1 tad.R1 -1.12.C. metallized resistor. 5 megobto.R2-Electrad potentiometer, 100,000 Min.R3-EInctrad potentiometer, 20 ohmsT-Thordarson transformer, type T-57361 Kurz -host+ vernier dial (large)

1 Aluminum panel, 7" a 12", 16 gauge,and 1 aluminum chassis, 11%.." by 8"by 1" high

1 Eby 2.gsits strip (screw terminals,1 Eby 2 -gang strip (tip jack terminals)1 Eby 5 -gang strip (screw terminals)1 Eby wafer type 4 -prong socket or Ham-

marlund Code S-4. Isolantite socketI D.P.S.T. toggle switeh

V-C3

(Ste TUT)

30 The HAMMARLUND

The Ray Five -MeterrrHIS three -tube super -regenerative re -I ceiver was originally described in de-

tail in "Radio News." It was designed byGam W. Ray, chief operator of StationWICC, Bridgeport, Connecticut, andowner and operator of an amateur stationwhere he has carried on extetIsive,eweri-mental work in the 5 -meterreceiver is the outgrowth of his experi-ments.

The receiver is constructed on an alu-minum chassis and panel for the sake ofthe shielding they provide. These aidin the elimination of hand capacity, andto further reduce this trouble, the varia-ble condensers are mounted at the rearof the chassis with long insulating shaftsand flexible couplings.

Coils LI and L2 consist of 6 or 7

turns each of bare round bus bars shapedon a pencil. After the receiver is com-pleted a little experimentation will de-termine whether 6 turns or 7 turns arerequired for each. The spacing betweenturns also plays an important part indetermining the frequency band coveredand a considerable amount of variationmay be obtained by spreading the turns.This adjustment will be facilitated if onecan obtain the assistance of a friend

ho has a 5 -meter receiver in operationwhich can be used as an oscillator ormonitor, in adjusting the coils to tht

List of PartsRAMMARLUND PRODUCES

CT-Midget variable condenser, type ME -20 -S

IA-Midget variable condenser. type MC -140 -M

C9.-. -Adjustable condenser, Isolantite insu-lated type MICS-140

3 Isolantite sockets. 5 -prong, type S -S2 Insulated flexible shaft couplina*, type FC

MISCELIANEOUS PARTS

Cl-Cornell condenser, .002 mfd.C2. C3. C:5-Cornell by-pass condensers,

.1 told.C4-Cornell condenser, .005 mfd.C6-Cornell condenser, .001 -tad..I-Single circuit (open) 'phone Jack1.1, L2, 1.3, 14, L5-(Soe test)RI, R2-I.R.C. Mg' taliced 2000 ohm., I

watt resistors113-1.R.C. nietalived 3-megolvm, 1 -watt re-

sistorR.1-Electrad type R1-205 potentiometer,

50.000 ohmsmetalised 200,000 ohms, 1 watt

resistorf-Thordarson audio transformer, type R-

26012 inch length, 34 inch diameter, bakelite

rod (for extension shafts)1 Grid clip2 Type .487 -While-I Typq111uminaiti for chassis and panel, 1/16 inchI 5 -wire battery cable1 Kurr4Casch vernier dial

Set

proper frequency range.The oscillator transformer L3 -L4 is not

particularly critical as to the number ofturns required. The specifications areshown below. The choke coil, LS,consists of 25 or 30 turns of No. 36silk -covered wire, spaced to occupy 3

inches on a piece of 14 -inch diameterbakelite or hard rubber rod.

8007 OF 52.361.1_ S.S.C. WIRE

"41-- SCRAMBLE WOUND

1 THIN-FIBRE

SMALL HARDRUBBER

-"TUBING

SMALL

SCREW &NUT

44007.0F N2.36 S.S.C.WIRESCRAMBLE WOUND

16N


The PentaflexIN spite of its tiny size, this receiver,

which was originally described in"Short Wave Craft," provides real 2 -tuberesults.

The method of employing a pentagridconverter tube such as the 6A7 to serve1.s both a detector and an audio ampli-fier stage is made clear in Figure 1. Herethe screen -grid section of the tube is con-nected like any other screen -grid tubeemployed as a regenerative detector. G4is the control grid, G3 and G5 togetherconstitute the screen, and P the plate.The triode section, used as the audioamplifier, employs G1 as its grid and G2as its plate. The cathode K is commonto both sections. The resistance couplingbetween the sections consists of R5 asthe plate coupling resistor, C4 as thecoupling condenser and R4 as the gridleak. The headphones are connected inthe circuit of G2 (the triode plate).

This application of the 6A7 tube ob-viously lends itself to compact receiverdesign and the Pentaflex takes full ad-vantage of this. The overall size is only7 inches long, 5 inches high and 3 inchesdeep. The chassis is formed from a 7

inch by 5 inch sheet of 16 -gauge alumi-num bent down 1 inch all around. Thisprovides deck space of 3 inches by 5inches after the chassis has been at-tached to the back of the 7 inch by 5

List of PartsHAW/1411E1WD PRODUC:TS

CI-Equaliser condenser, type EC -35C2-Midget variable condenser, type MC -

140 -MLI, L2-Standard set 4 -prong plug-in coils.

type SWK-41 Isulantite coil socket, type S-4, 4 prongs

MISCELLANEOUS

C3, C5--Cornell-Dubilier by-pass condensers,.1 mid.

C4-Cornell-Dubilicr by -pas, condenser, .01mid.

C.6-Arrolos pigtail micas condenser, .0001mid.

C7-Aerovo: pigtail mita condenser. .0003tad.

metalised resistor, 3 megohms1/z watt

R2-I.R.C. metalized resistor. 100 ohms,watt

113-Eleclrad potentiometer. 30,000 ohmsR.I, 115-I.R.C. metali,ed resistors, .25

ExteguitAli, 1/2 anti1 Ktirs-Kaseh vernier dial, small sisc1 Grid clip1 Toggle switch, d.p.s.t.1 Eby 7 -prong wafer type tube ocket for

6A7 tube, ur Hammarlund Code 5-711leolanthe socket

I Pentair: panel and chs.1-1.1 Eby 5 -gang strip (screw terminals)

Eby 2 -gang strip (screw terminals)I Eby 2 -gang strip (tip jack terminaly1

Rear View

Pond View

inch panel by means of 2 screws.The plug-in coils employed are the

standard Hammarlund 4 -prong type, fourof which are employed to cover the entireshort-wave range down to 15 meters.

Pis. 1

The HAMMARLUND 1936 SHORT WAVE MANUAL

INDEX

A Boy Scout's S.W. Receiver 8

A.R.R.L. "Ham" Receiver, The

Argonaut, The 99

An AC -DC 2 -Tube S.W. Receiver 24

Doerle 2 -Tube Receiver, The 18

.. 10

Gainer, The 28

Pentafleic, The

Power Pack for S.W. Receiver., A 12

Radio Amateur's Hand Book 3 -Tube Band Spread AC set, The 14

Ray Five Meter Set, The 30

Skyscraper, The 20

Three Tube S.W. Pentode Receiver, A ..... ......... ....... ....... 22

. . . The Hammarlund Snort Wave Manual containsan impressive array of receiver designs, each sound inprinciple. It should prove to be the "final authority"for those wishing to construct simple, yet efficient, setsfor short-wave reception. -1I. I,. llishlonian. Editor.1 /i-11-n re Radio.

. . . This, the third edition of the HammarlundShort Wave manual is truly an ideal book for everyshort wave enthusiast. rman Rornard, llanagingEditor, Radio World.

0

. . . Your new Short Wave Manual cannot fail toplease both shortwave "fans" and transmitting ama-teurs, containing, as it does, "how -to -build" data onmany practical receivers. -II'. MacDonald. ManagingEditor, Radio Retailing.

. . . The new Hammarlund Short -Wave Manual con-tains a number of practical and interesting receivers.

-Frank L. Britton. Radio Editor, Popular Me-chanics Magazine.

aUicrt. Bawl, Radio,

arnmarlundPRECIS/ON

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