Uses an autotransformer to generate huge sparks across a spark gap from 12v supply. Three pots let you adjust frequency, duty cycle and power for all sorts of effects.
At 50Hz the simulator doesn't show the back emf HV effect very well, slow it down to 10usec to see the calculation, swap the capacitors in the oscillator for 1nF to speed up the circuit to suit.
without the diodes on the +/- rails the clock multivibrator timing gets out of control from power surges, at worst case it'll smoke the transistors.
The RC tank under the spark gap is an X2 capacitor and a 1W resistor. This prevents the spark from causing a short circuit through the diode. This stops my power supply from tripping it's fuses when a spark occurs.
Other than that, it works fine. At high power the coil will self oscillate at its resonant frequency, and that's when power across the gap will peak. Using an accel super coil I was able to get a superb ladder arc to climb up from a 5mm gap. It was also throwing sparks easily across two needles in a 30mm spark gap.
