Building the poor-mans mini tesla coil ( slayer exciter)

Picture of building the poor-mans mini tesla coil ( slayer exciter)

A slayer exciter is basically a small solid state tesla coil, usually a one transistor design. The circuitry for it is simple. One of the first things anyone who has built a joule thief will notice, is that the circuitry is very similar. The biggest difference is that the small transformer or inductor has been replaced with a primary/secondary tesla coil configuration, and that the feedback is capacitively coupled. (There is a good abount of capacitance between the 'top' of the coil, and ground.)

There are many awesome thing these exciters can do!
they can:


  • neon lights!-----------------------------------------(several feet away)
  • florescent tubes!----------------------------------(within about a foot)
  • CFL's!-----------------------------------------------(within about a foot)
  • EL wire---------------(it does not work well for me. If anyone tries it, please tell me your results!)
  • LED's!-----------------------------------------------(across the room if done right)
  • and even small incandescent lights! -------(with an L3 coil)
  • paper with pencil markings -------------------(before it catches fire!)

Burn and ignite:

  • candles
  • wood (pencils)
  • human flesh (now my fingers smell burnt)
  • paper


  • crappy / half dead LED's
  • bacteria
  • sensitive electronic equipment (phones, computers, SD cards, CD's, blu rays, flash drives)
  • someone else's stuff


  • ion wind motors
  • the coolest lantern or light on earth
  • fires
  • plasma cutter

►Make following electronic equipment go crazy:

  • calculators
  • watches
  • digital clocks and alarms
  • devices with capacitive touchscreens (PlayStation VIVA, smartphones, feature phones, tablets)
  • UHF remotes

Transmit wacky sounds (loads of EMI) to:

  • AM radio
  • FM radio
  • shortwave radio
  • HAM radios possibly
  • TV interference

Here is how to make a my version of the more powerful exciter (These videos were made awhile after this intructable, so the only issue with it is thermal management.) Please do not get the instructions in this video confused with the instructions for the later TO-92 one in the further steps. Different bias resistor values should be used for either of these 2 versons.

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ok this time I've copied your plan to the letter with exception to the capacitors. As I can't find them in the city.

Still no luck.

Checking the battery voltage when connecting the system sees a 1volt drop

-max- (author)  robert.joyce.3136 days ago

What battery are you using? In my video shown in the instructable, I used a regulated 12V power supply that is capable of delivering 2A peek for a short duration, and 1.5A continuous.

So I assume you used a brand new MJE3055?

I bought a TIP41C transistor

I screwed a piece of metal to the back of it to act as a heat sinc

If the pinset on the TIP41C is the same as in your video, then they're setup the same.

I'm using a 9Volt rectangular battery.

Just tried connecting my 12Volt car battery.

Same. nothing happened.

On the power site of my 22k resistor, I have 12V, on the other side of the resistor I only have 0.5V

Is this correct? Doesn't sound right to me.

-max- (author)  robert.joyce.3136 days ago

That sounds perfect, the NPN transistor you have will act like a open circuit until you get to around 0.4-0.6V, where it will then start conducting electricity. It is like the minimum pressure you need on a check value to make it flow water the right way. Same for electronics.

Try a 1K resistor if the transistor is not getting warm. And also place a car flashing lamp or maybe a car head lamp in series with the 12V car battery to keep the current low in case of a short circuit or something. A car battery can deliver over 500A, which, if something is wrong, then the transistor will probably explode. Also, did you put any thermal paste on the heatsink? Radioshack will again have some of that if you need it, or online stores like Amazon.

ok I changed to a 1k resister.

I also checked every joint with an Ohm meter :) found a few try ones and fixed them.

This time when I connected the power, I got a spark when connecting.

The transistor started to heat up. But still no action on the light bulb :(

Oh, got my hands on a Capacitor too. but its only 100pF

Added this. after looking at a chart, seems like it's pretty small.

-max- (author)  robert.joyce.3134 days ago
Sounds great! Just follow the last half of step 8 for improving performance and you should be set! Try a few large electrolytic capacitors connected to where power connected as close physicly to the circuit.( as close to the L1 coil and emitter as possible. Keep the wiring as short as possible.)

steps? which part is step 8? it's not like they're labelled :)

-max- (author)  robert.joyce.3134 days ago

**Failure modes of operation, and how to fix them:** IF the transistor gets HOT, and it does not work well or at all judging by the neon lamp test:

  • This 90% of the time means that either:

    • A) The value of the bias resistor is too low, (try a higher value resistor)
    • B) The polarity of the L1 coil may be incorrect. (try switching the polarity)

  • IF the transistor is COOL to the touch, and does not work will or at all judging by the neon lamp test:

    • The polarity of the L1 coil incorrect. (try switching the polarity)
    • The bias resistor is too high a value. (try less than 10k.)
    • You have incorrectly built the circuit, (check and recheck the wiring)
    • Too many turns for the L1 coil causes poor performance (try less windings for the primary)
    • You screwed the pooch and killed your transistor

  • IF the circuit works, and the transistor is getting warm, borderline hot, but still does not function as well as mine:

    • Adjust the number of turns on the primary, or L1. I find 3-5 turns work will for 12V operation.
    • Adjust the bias resistor value, if it is too low, the transistor gets excessively hot. Too high, the circuit does not work well.
    • Try a different transistor, or one from a reputable brand, like Linear Technology, STmicroelectronics, Texas Instruments, ON semiconductor, or the ones you find on Jameco, radioshack (now bankrupt :( ) Digi Key, mouser, etc. Avoid the too-good-to-be-true deals on eBay. Often you will get hung-wan-low quality garbage, or old used and recycled transistors that have been cleaned up and the old part number of an inferior transistor scrubbed off and a new one printed on. Obviously you do not want that garbage.
    • You have the cravings for LOTS more radiation and EMI, try build a proper tesla coil! That is the next logical step up! :).

ok, so I'm off to buy a little neon lamp.

I have been using a fluro house light bulb and a torch that uses those little diode bulbs, but there was no result with them.

My Primary currently has 2 winds. Will try adding a wind.

I however, would not have thought there would be any effect given that it's insulated wiring you're using (and me).

I was using the 9Volt battery earlier as you recall. Last night when I fired it up, I was using that battery connector and just wired the car battery through it's contacts. The connector wire to the circuit board instantly caught fire and fried :) so at least now I know I've got a circuit.

I guess I better buy and hook up a car light bulb too right after the batter positive pole, as you advised.

-max- (author)  robert.joyce.3133 days ago

ONE LAST THING: If you ever suspect your transistor has been cooked, but are not sure, you can always google how to test NPN transistors. My favorite way to do this is to wire up a NPN transistor is in the "common emitter configuration" so as to use it as an electrical switch, and see if I can turn on and off LEDs or small lamps with it by applying a small current to the base by connecting the base, through that 1K resistor, to Vcc, the +12V.

I have two transistors, I did this test on both. They both show 1 when testing ANY combination of legs of the transistor.

-max- (author)  robert.joyce.3133 days ago

Post some photo's and pictures, even videos of your current build, so I can look over your wiring and what parts you have chosen. I can really help you much more if you do that, rather than teaching you all the electronics knowledge and how to test stuff yourself through long, boring comments. After all, a picture is worth 1000 words, and a video is 30 pictures per second, or equivalently, 3000 pictures per second! :)

I added some images but they've dissapeared.

Adding them again.

-max- (author)  robert.joyce.313yesterday

* You will ABSOLUTELY need a large heatsink, unless running on a 9V battery or less and getting hopeless performance.


* It seems like the wiring is correct, assuming the leftmost blue wire is the negative of the battery, and the wire closest to the matchstick is the positive, or maybe the bulb you have in series. HOWEVER, have you verified that the polarity of the secondary coil is correct? I always get this wrong when I build the circuit, even if I pay attention to the wiring!


* The only thing I would change is the capacitor for a larger electrolytic capacitor, or some beefy ceramic or film caps. The capacitance should be higher than 1uF, preferably higher than 10uF. Thats why I had so many capacitors in series with the supply.


One last tip: Try soldering a small wire that easily goes into the breadboard to the copper stranded wires, or cut away half the strands and solder them together so that instead of attempting to shove those PITA wires into place, and risk them shorting out with other stuff, they just insert easily.

BTW, when you mentioned there was a spark coming from it, did you mean like when the power was connected, that you got some yellow sparks (like grinding metal sparks, or sparklers) or did you mean a thin blue arc out of the top of the coil? (like the high voltage discharge from the top of the coil?)

well I have a little plate there at the moment to act as a heat sink. I'm only connecting it for a few seconds at a time right now while I measure with the meter. I'm getting .7v on the other side of the resister. Should be enough to fire off the transistor.

I'm getting 12V to the transister center pole.

I've tried swapping over the wires for the external coil too. No change.

Currently, the transistor isn't generating any heat at all.

Makes me think it's dead.

-max- (author)  robert.joyce.31323 hours ago

You can use the circuit here to test the transistor. However, the larger transistors need more current to turn on, and so instead of the base going to a finger to act like that pull up resistor in this circuit, you should connect the base to that 1K resistor, and have that go the the positive of the battery. Ans instead of an LED, use a small lamp (one rated the same voltage as your battery) and no 1K resistor that is in the video. (thats to prevent killing the LED.)

WOW, talk about overkill for testing a 50 cent transistor.

I think I'll wait till Monday then get a new TIP41C :)

-max- (author)  robert.joyce.31320 hours ago

lol thats fine too. I am impatient and want to verify if it is still working, so that if it is good, I do not lose time. :) It only take a minute to breadboard up a simple tester!

ok, a simple ohm meter test shows me that the second transistor, the new one that I bought, is dead before I even used it. Back to the shop again :(

-max- (author)  robert.joyce.31310 hours ago

I highly doubt that the transistor would be dead out fresh out of the packaging. Especially as rugged as they are. If you use an ohmmeter to test transistors, you really need to know what you are doing, and it helps to understand some basics of the transistor. (Compare this to when you first even looked under the hood of a car, without understanding much of anything, and spent a long time attempting to fix an issue maybe on your own without the help of someone more experienced, possibly making it worse. Surely this is happened to you at least once?)


Watch this video about how to test the transistor with a ohm meter, or I recommend just building the circuit I described earlier. This method is tedious, and not particularly easy, but if you really want to use your ohm meter, make sure to measure it correctly.

ok, now I've got two good transistors.

but they aren't getting hot.

-max- (author)  robert.joyce.3139 minutes ago

Well they shouldn't get hot if you have the heatsink, with thermal paste. (that is necessary stuff. The heatsink is pointless if you cannot get the heat from the transistor to it.) That said, Do you have a picture of the entire setup, including the bulb? I suspect the bulb you have in series is too small a wattage, in which case it is absorbing all the energy, and dropping away all the voltage, leaving hardly any voltage for the exciter. The voltage across the slayer should be around 11-12V. If it is, then the bulb is probably dim because it is only dropping 1 or so volt, and very little current is flowing, in which case, a smaller value resistor is needed. (though it is already really low, I can not imagine why it would need to be lower.)

ok the transister is fine.

however, when I test the voltage on the other side of the little light, I only see 1 volt coming out. I replaced it with a resistor, same result, only getting 1 volt on the other side of it.

-max- (author)  robert.joyce.31310 hours ago

If you are using a digital multimeter, I recommend at using the diode test function. It is explained 1/3rd of the way through the video.

The car lamp lights too, so I'm getting a 12V circuit

hahah ok I blew up a transistor. nice little bang. Scared the crap out of me :D

I'll get a pic to you in the morning.

-max- (author)  robert.joyce.3132 days ago

I had a voltage regulator blow up in my face too, a good sized chunk came out and hit me in the face! I learned the painful way that the LM137T does not have the same pinout as a 78xx regulator!

-max- (author)  robert.joyce.3132 days ago

That why it is nice to have a resistive load in series with a supply if it is really low impedance output, and capible of delivering lots of current!

-max- (author)  robert.joyce.3133 days ago

To test a transistor with a multimeter and understand what it is telling you, you need to know how the NPN BJT transistor is made, and how to use them, and stuff. Some meters have a transistor tester built into them, and there are tutorials to build a NPN transistor testers. Some of the advanced ones can even measure the specs of them, like HFe!


OK here is a easy quick way to test the transistor without the multimeter: Assuming you have wired up the circuit correctly, and you still have the lamp in series with the whole SEC (Slayer Exciter Circuit), take out the connection feedback from the secondary coil (that thin magnet wire from the big tower coil) and with a 1K pullup resistor still connected, the bulb should come on at very near full brightness, or full brightness. When you remove that resistor, so that nothing at all is connected to the base, then the bulb should immediately go out completely. If it does not, replace the transistor. Again though, make absolutely certain it is wired with the correct pinnout. This should be the correct pinnout for the TIP31C:

-max- (author)  robert.joyce.3133 days ago

I think I am being a bit harsh to 9V batteries, although they will sometimes technically work, I still really hate them for poor performance... you get the circuit working with it, but not very well because of internal resistance is pretty high and even when completely unloaded, it is only a little over 9V when fresh. 8 AA, C, or D batteries in series is not a bad source of power.


I should mention before you buy anything, that a high power(4-6 ish ohm) resistor in series with the 12V car battery should also work to limit current, if you so happen to have one laying around. You could even use a thick pencil lead too! (Note it will get very hot if lots of current goes through it, it may glow cherry red or orange, and burn off the wood. But it works! :) )


Adding a small amount of ESR to a big 12V battery is ideal, it means the voltage will sag in relation to the current drawn, but it keeps you from melting wires and making stuff explode! Good for prototyping until you get the thing working well enough to not need it!


Idealy, a 12V "CV" power supply w/ 2A standard CC limit should be used. (those old, really big and heavy wall adaptors w/ around 12V output will should work nicely, even though they are not regulated outputs)

ok well I hooked up a small brake light globe to the positive circuit inbetween the board and the battery. On the Battery side of the globe I have 12V, but on the other side of the light, is only 0.35V so, as expected, nothing works.

Now I'm going to try the 5.1kOhm resistor I bought today to see if that works or fries.

Man... how can this be sooooo difficult?

-max- (author)  robert.joyce.3133 days ago

I presume your lamp is at full brightness, and it means there is a short circuit. If the transistor is still good, that means if you remove the resistor that is turning on the transistor, then the lamp should go off on it's own. (If the lamp is on even when there is nothing connected to the base, then you need to get a new transistor.) In that case, try reversing the polarity of the L1 coil and reinsert the resistor.


You may consider using a variable resistor, or a trimmer, or a POT (these are all basically small rheostats.)

-max- (author)  robert.joyce.3133 days ago

Well this is why it is good to know the theory of operation, which does require some easy fundamental physics. (I know it sounds indimitating, it was for me, but it really is not that bad if you learn it the right way.)

-max- (author)  robert.joyce.3134 days ago

Alternatively to the neon lamp, you could use a avramenko plug, and it is more sensitive. It is simply 2 diodes in series with a LED or other load, with an antenna connected to an arbitrary node on it, and your fingers or a ground, or something capacitively coupled to ground connected to another arbitrary point on it. You do need to harvest an LED for that though. I like white and blue LEDs.

2 windings is probably not enough. Think around 3-6 windings.

-max- (author)  robert.joyce.3134 days ago

There are 9 steps total in the 'able, and the last 3 are troubleshooting the weak and strong variation of this circuit, and a picture gallery of my original one. Step 8 is troubleshooting. I think instructables has changed the desktop version to be all steps on one page, though on mobile it is steps you have to keep clicking through.

-max- (author)  robert.joyce.3136 days ago

Whats confusing about this instructable is that it is a bit fragmented. I have 2 versions of the circuit built up, the older version, for which I used a few 2N3904's, and it is not very good, and also the version in this video is better.

This is the video that I used to make it.

The capacitors are the only thing missing.

What about the voltage on the other side of the resistor? Should it be so low?

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