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I recently built this tesla coil, and I've tried many different setups, but for some reason, I can't quite figure out why it won't work.

schematic

simulate this circuit – Schematic created using CircuitLab

I also have a few pictures that I took to show what I have. The 9volt is charged. I double checked the leads on the transistor, I don't know what could be causing the problem.

image1

image2

image3

image4

The last picture is before I added the 2 rectifier diodes.

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  • \$\begingroup\$ I am uncertain of intended action BUT - Polarity of secondary to primary matters. D1 D2 need to conduct when secondary "fires". If my understanding of ooperation is correct - transistor base is driven negative when firing - so BOTTOM of primary winding shoukld go to transistor collector. You have TOP going to collector. \$\endgroup\$ – Russell McMahon May 15 '19 at 13:16
  • \$\begingroup\$ Here is coil that someone else built: instructables.com/id/… It seems to be basically the same as yours. The coil polarities are critical. \$\endgroup\$ – Mattman944 May 15 '19 at 14:37
  • \$\begingroup\$ Your solder joints are terrible. Copper oxidizes and will not solder well. Use fine sandpaper or a knife to scrape the oxidation away until the copper is bright and shiny before you solder. \$\endgroup\$ – Mattman944 May 15 '19 at 14:38
  • \$\begingroup\$ The 47K should go from base tp V+ ||| In your modified circuit you failed to keep the base to +ve resistor where it belongs. You now have it going from base to collector - as soon as the transistor starts to turn on it reduces base drive and the transistor enters a stable low current state. \$\endgroup\$ – Russell McMahon May 16 '19 at 10:52
  • \$\begingroup\$ Is the copper wire that you are using "insulated" ? ie has it got a thin coating (enamel or similar) on it that prevents electrical contact being made when you touch anything to the wire. The wire MUST be insulated. \$\endgroup\$ – Russell McMahon May 20 '19 at 7:27
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Polarity of secondary to primary matters.
D1 D2 need to conduct when secondary "fires".
Transistor base is driven negative when firing -
so BOTTOM of primary winding should go to transistor collector.
You have TOP going to collector.

Swap connections to primary winding. Stand clear.

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Added:

The 47K should go from base to V+

In your modified circuit you failed to keep the base to +ve resistor where it belongs. You now have it going from base to collector - as soon as the transistor starts to turn on it reduces base drive and the transistor enters a stable low current state.

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  • \$\begingroup\$ I have performed the revision, but still not lighting up the light bulb. This is how it looks after revision. imgur.com/uclbsVA Any help is greatly appreciated! \$\endgroup\$ – Anhedonian May 15 '19 at 14:01
  • \$\begingroup\$ Yes, when I swapped the leads of the top and bottom of the primary coil, i forgot to switch over the resistor to the V+. I've done that now, and it still doesn't work. I'm starting to think I may have fried something along the way, because now everything should be correct but the light bulb isn't responding. imgur.com/rpMTxlN \$\endgroup\$ – Anhedonian May 16 '19 at 19:26
  • \$\begingroup\$ @Anhedonian A dead transistor is the most likely thing - but it shouldn't have been killed by what you did. Check your solder joints are OK (they are less pretty than they could be. And general layout could easily be quite a lot tidier. | TIP31C datasheet here - The current gain is low - 10 to about 50 depending on colour grouping. ... \$\endgroup\$ – Russell McMahon May 17 '19 at 12:05
  • \$\begingroup\$ ... Base current via the 47k is about 0.15 mA (SMALL!) so collector current is about 1.5 mA (tiny) to under 10 mA (still tiny). I'd think a 4k7 base resistor or even smaller would be in order. | What is your MEASURED battery voltage? \$\endgroup\$ – Russell McMahon May 17 '19 at 12:05
  • \$\begingroup\$ I dont have a voltmeter so i dont know, but im using a standard duracell 9v. I swapped 47k resistor to a 20k resistor, and I also swapped the 2 rectifier diodes to an LED diode. The LED isn't lighting up, but I can feel the transistor starting to get kinda warm. Still no light bulb response. I moved the setup to a breadboard for a clean solder-free circuit haha, here is how it looks now imgur.com/uPTrZmd I KNOW the circuit is right, but for some reason, I'm not getting a reaction \$\endgroup\$ – Anhedonian May 19 '19 at 6:12

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