Nelsress, just a quick question: The 331C shows on the front face plate as being a 'stereo tuner'. Also, I note what looks like 'pairs' of outputs. While I'm confused about the fact that it may have a 'pre-amp' function contained within that is 'mono' only, still seems to me that if this IS a stereo tuner, then perhaps you might consider questing for another 240......and a nice 'pre-amp' of sorts. Don't you just love it when other people spend YOUR money!!!.........lol. Anyway......I've heard that the real issue is that a tube rectifier doesn't start conducting until the filaments get hot....and that doesn't happen until around 40 or 50 volts....depending on the unit. I ALWAYS pull the output tubes when doing this!! I bring up the unit on Power Supply Only.....and check B+ voltage along the way. Not all units have a tube rectifier.....so they are putting out B+ as soon as they are turned on. My understanding is that re-forming of the caps.....'IF' it can be done, will start as soon as the B+ hits them......and takes about 2 to 3 hours or more at any given voltage. So, at 40 VAC on your variac, and w/ a tube rectifier....you may start heating up the rectifier filament and start passing B+...which may only be about 150 volts at that point....but that's still enough to start re-forming a bad cap......or, start warming up a shorted cap...which is why you need to pay close attention to the temp of the power transformer AND the caps in the circuit while you do this process. If EITHER start to get more than just a 'warm' ..... then you need to shut down. Another good idea before you do anything is to pull the rectifier and all the other tubes and just turn the amp on and check the transformer voltages first. If you have the proper secondary voltages from the PT....including the filament voltages AND secondary voltage...then just let it run 'idle' for an hour or so and make sure it's not heating up. If not.....THEN start with the variac stuff. Rectifier first. Then once you get to about 90 vac, shut it down and install the other tubes. MAKE SURE YOU HAVE A LOAD ON THE UNIT.....either dummy loads or test speakers. I start with dummy load and shorted RCA plugs on the inputs. I run at 90 volts on the dummy loads and check for any temp increase on the Output transformers AND the dummy loads. If the amp is self-oscillating you may start building heat in the dummy loads. If no indication of a problem, I un-ground the input and run it for another hour or so that way. And, if no problem, I switch to test speakers. If they run quietly, I apply a 'source'. I have some inexpensive signal generators I bought off ebay for about $20 each....but they'll do 10 volts RMS from about 20 to 20......maybe a bit less.......but still...........perfect for my purposes. I just run 0.1 volt into the amp at 1Khz........sweep around the frequency range a bit.....and if all sounds good........I put the dummy load back on the amp and leave it oscillating at 1K for another hour or so. Then, I kill the signal and finish off by bringing the amp up to line level AC voltage. I too have never suffered a catastrophic failure....but I HAVE found plenty of amps that needed further repair in one area or another. This may be a complicated process......but it works for me. And......I trust it! For what it's worth!!...... Tom D.
