Hello All: With AC resonant charging, the maximum attainable voltage is pi times the peak AC voltage. This can occur after 1.75 cycles of the AC. If your spark gap is set to fire every 1/2 cycle and misses a couple firings, the voltage can rise to extraordinary values: 10 kV x 1.414 x 3.14 = 44.4 kV peak! (So long, NST!) Regards, Mark S. Rzeszotarski, Ph.D.