Quoted from Oldgoat:I was thinking a capacitor; however, the way the machine works is you grab two handles, one of which turns. As you turn the handle, a coil moves on a rod over another coil causing the voltage to increase.
Yes, variable transformer. Does this machine plug into A/C mains? Or did it operate off battery?
If battery, then there must be some sort of "chopper" circuit. Transformers don't work with D/C.
Many years ago, I took apart a vacuum tube car radio (note: NOT stereo ) It had a part in it (called a vibrator, IIRC) that would switch the 12DC from the car battery on and off very rapidly so it could be fed to a transformer to get the high voltages needed for the vacuum tubes. If your machine operated off battery, then I suspect it used something similar. If so, my best guess is it is a capacitor that went across the contacts of the vibrator to prevent arcing which leads to contact erosion.
If it works on A/C, then all bets are off and I just made everyone suffer through a history on vintage electronics for no reason.
Best of luck.