I figured this would be the better place to post the following question than the Technical section. First off, even though I'not a pro I've fixed a couple of amps that I've bought dead, capped/serviced all of my own and some friends' amps, and built a few amps so I know the correct answer to my question is "use one method or the other", but what happens if you use the PT's center tap and the artificial ground reference resistors at the same time when hooking up the filament heaters? I just picked up a 1969 Princeton non-verb. I already own one and a '67 PR plus have sold a couple in the past, and I knew this one had been worked on before. When I finally got around to open it up a few days later I discovered that both the center tap on the transformer was grounded and it had a pair of resistors soldered from the power lamp to ground. It already has a properly grounded three-prong cord added, the death cap removed, and the polarity switch disconnected and is one of the quietest idling amps that I have. I've usually heard that if there's a center tap that it should be used (the way method I follow) and I've also seen some recommend try both methods separately and use the quietest, but I've always read that you never use both methods together. If this amp has been used this way for over a year should I expect any issues and what are the possible ramifications of the heaters having been run this way? All the plate resistors have been changed and it appears that the artificial center tap resistors were added at the same time. The PT is a Classic Tone replacement which was already in it when the previous owner bought it. I knew what I was buying in that respect and knew that the PO had had a couple of minor issues, but planned on doing some minor mods and having to do a cap job anyway, although all electrolytics except the can have already been replaced. Any info on having the center taps both hooked up at the same time? Thanks.