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ponents.Stort by drilling holes in the enclosure

to pass wires through ond for the ponelmounted components. In the outhor'sprototype, three sides of the enclosurewere outfitted with appropriate sizedholes. A %-inch hole wos drill in one sideof the enclosure, through which oground wire connects to L3.

On onother side of the enclosure,holes were drilled to occommodote o

dowel rod (which is port of the stotionory spork gop), o fuse holder, ond thepower cord. On the third side, threeholes were drilled for banano jocks. ltwill o so be necessory to drill holes in thebottom of the enclosure suitoble for T smounting hardware.

Begin ossembly by mounting thepower tronsformer on the bottom ofthe enclosure. Next connect o 10-f.LHACfilter choke in series with eoch of T1 ssecondory leods, ond then connectthe free ends of eoch coil ocross C1see Fig. 1).

Note: In the outhor's prototype, C1 isreolly two .012-f.LF.2500-volt AC copoci-tors thot were wired in seri es to createC1 (giving the copocitor an effectiveroting of .006 f.LFot 5-kV AC). lf you usethe some scheme, keep the con-necting leods between the copocitorsos short os possible. After connectingthe copocitors together, cover the go pbetween the two units with non-conductive tope, ond connect the jerryrigged unit in the circuit os shown.

Stationary Spark Gap The stotionorygop con be mode from two 3/16-inchcorrioge bolts see Fig. 3). One bolt isstotionory ond the other one is odjustoble so thot it con be used to vory thespork gop. A Y2-inch wooden dowel isottoched to the bolt thot is to be od-justoble, ollowing odjustments to thego p to be mode from outside the projecfs enclosure.

The wooden dowel is very importont:one does not wont to odjust the go p bytouching metol (or ony other con-ductive device), since the gop is od -justed with the Teslo Coil in operotion.

The bolts tho t form the spork go p oresupported by two T brockets mountedto spocers so thot they foce eoch othersee Fig. 3). The stotionory post of the

spork gop is connected to J3, ond themovoble bolt is connected to J2.

Primary Coil The originai primory coiL3) wos mode from 6 turns of #16 olu

minum grounding wire in o poncokestyle winding. However, to give the unit

3 16 INCH CARRIAGEBOLT

L BRACKET

1 2 INCH / FUSECERAMIC HOLDERSTANOOFF

Fix. 3. The stationary .1park xap is made from two 3/io-inch carriage bolts supportedby L brackets mounted to spacers so that theyface each other. One bo/t is madestationary, while the other is made adjustable so as to vary the spark gap.

NOCONNECTION

Fix. 4. The inner windinx (Jf L3 should ha ve an area of about 6-inches square. When makinxthe coi/ he careful t ha t you do notj1rm w re loops, instead of the continuous coi/illustra ted h ere.

o somewhot unusuol look, the originai(more-or-less round) primory coil wosreploced with o squore version modefrom heovier #10 oluminum groundingwire. The Coil wos formed on four 6-

position. twin-turnscrew type borrierblocks, which were mounted on fourblocks of wood.

The wood blocks (with borrier blocksottoched) were mounted to the top of

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the enclosure near the edges, and b1Jswire was then connected to the barrierblocks to form the coil. Note: The wiresdo not have to be fed through the barrier strips because of the twin-turnscrewarrangement. The wire con be cut tothe proper size and screwed into theterminai strip to form the primary coil.

The inner dimensions of L3 should beabout 6-inches square. When makingthe coi be care ui that you do no form

wire loops. instead of the continuouscoil illustrated in Fig. 4. When you arefinished with the coil, there should beone unoccupied screw terminai at thecenter and another at the outer rim ofthe coil. The unoccupied terminai atthe outer rim of L3 is connected toground via a wire that's brought outthrough o hole in the enclosure. Theunoccupied terminai at the center ofthe coi is left floating.

The Secondary Coil To fabricote thesecondary coil (L4). the author woundabout 348 turns of 24 mognet wireonta an 8Y2-inch length of 3 -inch diameter PVC tubing . That works outto beabout 48 turns per inch, covering 7%inches on the PVC tubing.

The coil was wound by hand using osimple j ig-which consists of little morethan a stand for the wire and anotherfor the coi form. When winding the secondory coil. try to keep the winding oseven as possible without overlappingany turns.

After the coi has bee n wound. applyclear varnish or polystyrene (Q-DOPE)to hold the coil windings in piace, andto hel p insulote the coi Next drill o smallhole in the center of the Tesla Coil enclosure l d, an d thread the lower leo d ofL4 through the hole ond connect it tothe ground end of L3 (os shown in Fig. 1)ond mount L4 in the center of L3 (seeFig. 4). The secondary coil is then secured in piace with glue.

s an odded measure of protection,you con olso piace clear plexiglass 4-inch OD (outside diometer) tu bing averthe secondary coi osa second loyer ofinsulotion. You might also seol the insulating tube ond piace minerai oil1n it,thereby further increasing the tubing'sinsulating properties, but that's not necessory for this type of Tesla Coi

The Output Sphere The outputsphere-a 1 -inch steel bal i on top ofo plostic spacer-also serves os the topcopacitance. An important point hereis thot the surface area represents thecapacitance not the inner area of the

Fig. 5. The rotor oj the rota n spark gap is m ade from a sma/1 pcrfbo rd square colltainingfour 6 screws t ha are connccted through bare bus w re. The st tion n post consist of anotlu:rperfboard square (o( equa/ size , containing two 6 screws t ha are notti ed togetherrlectrica/IY.

bali. lt matters not if you use a solid bolior a hollow bali: they will both workequally well os long as their surfoceareos are equal.

The size of the sphere effects the secondary's resonant frequency, so if youuse o lorger sphere, it will be necessaryto retune the primary coi for maximu moutput. A bigger sphere collects moreenergy, causing it to give o a higheroutput. So experimenting with the topcapacitance is highly recommended.

The Rotary Gap The rotary spark go pis not necessary to the operati o n of theTesi a Coi So, if you do not wish to buildthe optional rotary gop, skip this section.

The rotar of the rotary spark gap ismode from a small perfboard squareon which four 6 screws are mountedand electrically connected throughbare bus wire. The stotionory post consist of another perfboard square (ofequol size), containing two 6 screwsthat are not tied together electrically.The screws of the stotionary post areinstead taken out to J4 and J5. Perfboard is specified because the holesin perfboard make it easy to align thescrews on the rotar with those on thestotionory post.

The first step in building the rotory

gap is to build and mount the motorsupport. In the author's prototype (seeFig. 5), the motor mountwas mode fromsmall blocks of wood assembled in aU shope. A wooden mount s al so used

to secure the stationary post in piace.The distance between the rotar

screws and the stationary post screwsmust be as small as possible withouttouching in arder far the unitto functionproperly. After mounting the motormount in the enclosure, piace themotor in the mount and secure it inposition with epoxy.

Next assemble the motor controllercircuitry on a piece of perfb oard , usingFig. 2 as a guide. Note that T2, R2, J4,and J5 oren't mounted to the perfboard, but instead ore mounted to therotory-gap enclosure. Once the controller board is assembled check yourwork for wiring errors. lf ali checks out,solder wires to the appropriate pointson the boord for connection to the -board components. Set the boord tothe side for now: it will be installed in amoment.

Mountthe off-boord components onsome convenient spot on the enclosure. Mount R2 so that you'll haveeasy access to its wiper. Jocks J4 an d J5con be mounted in any desirable l oca-

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TESLA COIL

tion. Before mounting T2. make surethat the transformer leads are longenough to connect to the perfboardassembly.

After mounting T2 in the enclosure.mount the perfboard assembly on theenclosure using standoffs. and thencomplete the wiring between the perfboard assembly and the off-boardcomponents. With that done. plug inthe line cord and rotate the wiper of R2.making sure that as you do the motorspeed increases and decreases. lf thecircuit does not operate as described, itwill e necessary to recheck your work,correct any errors found, and try itagain. lf everything checks out. the ro-

grounded. You must use a 3-conductorAC power cord that is grounded ( earthgrounded) in the Tesla Coil itself. o nottouch the Tesla Coil while ifs in operation. However if you want to show-offyour creation, a fluorescent lamp maybe placed near L4 to demonstrate theionizing power of the Tesla Coi

Only use properly rated components. Do not use an overrated powertransformer. A 3-kV transformer with a 2-kV AC capacitar is out of the question.An overrated capacitar (for instance. a6-kV AC unit) is fine in the circuit. -member the capacitors are AC ratednot DC rated.

The rotary gap will work well with thisunit, but it may not work well with alarger unit. A larger unit will require thatthe rotary gap be redesigned. You must

Here's an inside view o the rotary spark f?Gp note the tight spacing hetween the perfboardrotor and the stationary post. The wires comi n[ from the stationary post are connectedto 14 and 15, throuf?h which the rotary spark gap is connected t o the Tesia Coi circuir.

tary gap is complete.

Caution The most impor tant part ofusing the Tesla Coi is safety. Never tu ne(adjust the tap on L3) the Tesla Coilwhen power is applied to the circuit.Use a phenol ic plastic box or a woodenbox to house the Tesla Coil and the rotary gap--avoid metal enclosures likethe plague. In addition. it is recommended that you use one hand on ywhile working with high voltage, andwear rubber soled shoes to reduce thepotential of shock hazard.

The power transformer, capacitar C1,and coils L3 and L4 must be properly

also protect your eyes: Do not stare atthe stationary or rotary spark gaps;doing so can cause eye damage.

Operating the Tesla Coil. With theunit completely assembled. make surethat ali the components are properlyinstalled and oriented. lf you are usingthe stationary gap, start with a gap distance of about a inch and tu ne L3 atany point on the third turn from ground.At that point turn the power on; youshould get an output at the sphere. Adjust the spark gap for maximum output.

lune L3 far maximum output, bychanging the position of the alligator

clip with the power aff. Tuning L3 andadjusting the spark gap greatly effectsthe output of the Tesla Coi lf you piacea grounded wire near the outputsphere. you should get 3- to 4-inchsparks.

lf you are using a rotary gap, makesu re tha t the screws o n the rotor an d thescrews on the stationary post are asclose as possible. Remember. thespeed of the motor effects the output.so adjus tthe motor speed with the variable power supply.

There should be no arcing anywhere.Ali arcing must be corrected or you'llburn au t the turns in the secondary. lf L3is too close to L4. arcing con occur. Youmay piace a 4-inch OD plexiglass tubing aver the secondary coil to help prevent arcing between L3 and L4.

Be aware that corona discharge (abluish-purple ionization. of the airaround the Tesla Coil) con causebreakdown olang the secondary coil,and loss of power at the output of thesphere. Proper insulation of L4 will limitcorona discharge. You may also noticean output at the top of the secondarycoil coming aut of the sides. That willtake away from the output at thesphere. you could piace severa layersof tape (Turn off the power first ) aroundthe upper-portion of L4, until the outputfrom the sides of the Tesla Coil is reduced.

In operation. the Tesla Coil emitsozone gas. which in large quantitiescon be dangerous. So use the Tesla Coiin a well ventilated room, and do notoperate it for periods of more than 3 to5 minutes at a time.

In addition. the Tesla Coil emits a fairamount of Radio-Frequency /nterference (RFI). Coils L1 and L2 help to limitthe amount of high-voltage kickbackintroduced to the AC power line. andhelp to prevent the high voltagekickback form damaging the powertransformer. Even with such precautions, RFI will stili be generated at thespark gap and the output of the TeslaCoil. RFI will effect both AM radio andtelevision reception. That's why youshould not operate your Tesla Coil formore than a few minutes.

The Tesi a Coil is an excellent introduction to high-voltage, high-frequency,and tuned circuits. And after buildingthis one. you may wish to build a largerunit. The author does not recommer,dbuilding a larger unit until you velearned enough about such circuits.and the safety precautions that mustbe followed when using them.