I've been playing around with the well-known slayer exciter, and trying to make a tesla coil.

The standard 1 transistor setup works fine for me, but the arcs I'm getting are pathetic, and it can only light up about half of a CFL bulb.

I tried replacing the transistor I was using (BC548) with a larger power NPN (BUL310PI), which stopped the circuit working altogether.

Since the circuit worked with the smaller transistor, I thought it was either to do with the larger transistor being too slow or having too low an hFE value.

I thought if I used the BC548 to drive the base of the BUL310PI, I could overcome the gain problem if there was one.

The LED I was using for a diode lit up when I did this, so I had oscillation working again, but the coil couldn't light a CFL or make arcs. The LED also dimmed whenever I brought my hand close to the topload.


The transistor on the left is the BC548, the one on the right is the BUL310PI.

I've used 8 turns for the primary, ~300 for the secondary, and a large cardboard circle covered in aluminium foil for the topload.

I'm running the circuit off of 5V from an L7805.

I've tried all the usual slayer exciter troubleshooting gubbins, i.e switch primary connections, add/remove turns, etc.

What else can I do to make this work?

  • \$\begingroup\$ Your picture link is broken. \$\endgroup\$ Commented Aug 7, 2018 at 23:39

2 Answers 2


The Darlington pair is concerned that its speed is very slow. Especially the turn-off time is too late. So you should use the totem pole as shown in the figure for speeding up. enter image description here


The energy stored must equal the CFL rating and for this we need to know L, and f.

But for a rapid flyback effect, Q2 needs a faster decay time to turn off. This add some resistance across Vbe of Q2. ~<10k

  • \$\begingroup\$ Stuck a 1K from ground to base of second transistor. No change, sorry. \$\endgroup\$ Commented Aug 8, 2018 at 0:26
  • \$\begingroup\$ Have you tried 9V battery? Can show coil? \$\endgroup\$ Commented Aug 8, 2018 at 0:50
  • \$\begingroup\$ I have. I also tried ~14V, which improved only the circuit's hand-warming capability. \$\endgroup\$ Commented Aug 8, 2018 at 0:58
  • \$\begingroup\$ How does appearance of air coil compare to those that work? \$\endgroup\$ Commented Aug 8, 2018 at 15:45
  • \$\begingroup\$ It's wound around a piece of PVC pipe with about 1.5 inch diameter. The length comes to around 5.5 inches. I've seen both larger and smaller coils working with the same wire gauge. My topload is larger than anything I've seen, but putting on a smaller one doesn't help. \$\endgroup\$ Commented Aug 8, 2018 at 17:36

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