7.5 cycles per second = 7.5Hertz
If the pulse is a 50% duty cycle, then during the off time of the duty cycle, you have enough time to pulse some HV pulses in the cell.
It takes 10 to 15 milliseconds for the magnetic field to reach maximum strength for ignition coils...
Herman wanted 70KV, so he needed that well build up magnetic field.
So, here is the math:
13ms = 75hz.
It means that during the off periode of the 7.5hz cycle, Herman could pump 5 till 6 HV pulses into the cell.
cheers