Just a thought on the Variac:
It seems to me that most (if not all) of the talk surrounding Ed's use of the Ohmite Vari/AC ignores the need for re-biasing the 6ca7s to compensate for drastic, and even nominal, changes in wall voltage. If Ed ever dropped to 70 volts, his amp would surely sound like crap without being re-biased, and there's an upper limit involved here. That's pretty low input voltage and really not very practical, but I'm not ruling it out.
Nevertheless, I do think that Ed would have caught on to a slider resistor out of practicality and, if he himself was doing the re-biasing, it would be practical to have outboard taps and bias control, otherwise he would be constantly, needlessly, wasting time pulling the chassis before a gig and risking death shock. Highly-charged capacitors and delicate benchwork don't mix well with hard partying or rushing to play a gig. Better to have those capture nuts welded or soldered in, too.
