Sorry, a few mistakes in the posting... > prim: > primary coil is about 5 turns 1/4" dia copper tube, The coils inner diameter is really 8,5cm, start to end is 7,5 cm so the outer diameter is 16cm. The coil's a flat spiral. In size it is a little smaller than the top toroid, which btw is 24cm above the primary coil. Is 763kHz resonant frequency too high? For a cheapo spark gap? thanks, Florian