This is my current controller. It consists of a start button, a kill switch, a GE 600 vac 90 amp motor starter, a 120 vac 17 amp Superior Electric Powerstat (see modifications below), 154 mF 370 vac capacitor bank, a 120 vac 45.8 amp Superior Electric Powerstat, and a 600 vac 30 amp 3 phase Emission Control EMI filter.
This is my 120 vac 17 amp Superior Electric Powerstat, which I modified for 120 volt in, 0 - 140 volt out. Fortunately, this variac already had a tap in the middle of the windings for 60 volts in or out, which meant I already had four terminals. I simply counted the number of turns, did a little math to determine where I wanted my new tap point, confirmed this location using my DMM on the wiper portion of the windings, then stripped and soldered my new tap point. Actually, once I determined where I should place my new tap, I noticed that the winding was already waiting for my wire, as it had some insulating material already in place to protect it from adjacent windings, just like the tap point I was abandoning. This can be seen on the above photo.
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