I've got an old Gibson I use for a hobby, the thing has never been right . Heavily and badly modded when I got it, blown caps and trannies, the whole bag. 6eu7 preamps and EL84 outputs, push-pull. Reverb & trem, but that's irrelevant. Pair of diodes for rectifiers, with some small resistors and caps on them to kill switching noise. Got a bad 120 Hz hum, as soon as I come off standby. Scope shows grid input on the EL84's at just about flatline, there's a little noise on the screens, but not much, (huge choke in the power supply just before the screen, but after the power tube plate supply). We're looking at the typical setup, power trannie has two leads that go to the diodes, and a center tap from that winding to ground. DC + side of the diodes goes to + on an 80 uf cap, other end of cap grounded and connected to the centertap lead. Cap + hot lead goes to the center tap on output trannie primary, other output primary leads go directly to plates on the EL84s. Output secondary goes to the speaker, there's no ground at the jack, its isolated. (tried a ground there, no difference). Going hunting with the scope, we see a huge 120 Hz sawtoooth at the diodes, kinda what I'd expect. At the cap +, and at the plates, we see a much smaller, but identical sawtooth. At the speaker jack, we see a sort of rounded smoothed version of the sawtooth, fairly big, and that;s what I'm hearing. Now, two questions.... As I understand it, in a push-pull amp like this, the noise on the plates from the powersupply should be out of phase and cancel each other as far as output noise. Maybe not perfectly, but my rig isn't doing it at all, and it looks like the plate noise signals are IN phase. Am I crazier than usual, or is this quite weird? Second...that sawtooth at the cap + end and the plates....its the same waveform as at the diodes, just smaller. I'da thought it should be smoother and rounder and flatter than the waveform at the diodes. Tried different caps, alla same, no mo betta. Any ideas what I'm dealing with here, (besides my ignorance?) Could brute force it, with a mongo choke on the plate B+ line, but I'd much rather know what's really wrong and fix it properly.