I don't think it's possible, or at least it's not recommended, to
set the timing of a SRSG solely on the basis of the AC mains
phase. The right setting will be highly dependant upon capacitor
size, NST current, Variac setting, ferroresonances in your NST, and
perhaps phase of the moon ;-) It's typical to set the SRSG phase
experimentally, just adjusting for best performance. It's best to
vary the phase in real time while the coil is running, either by
mechanically rotating the motor in its cradle, or by using John
Freau's phase shifter circuit and just twiddling a Variac knob. I
find that the SRSG phase is an extremely critical setting and I
wouldn't dream of locking it to any particular setting.
Regards, Gary Lau
MA, USA