I had a similar experience: noise in the clean channel (dirty channel was quite quiet). I tried a bunch of the same things that CapnDenny tried but they didn't help. (Added more power supply filtering, moved wires, replaced jumpers w/ wire, snubber caps across my rectifier diodes). The one thing I noticed was big ripple on V+ supply... I think I recall amost 5Vp-p of ripple on a ~400V supply. When I pulled the heater filament cable harness off (while powered down, then reapplying power), the V+ was flat as could be. So I wondered whether the filament current demand was injecting noise into the power supply via the transformer. So, I added a standalone 6.3V CT filament transformer (a pretty cheap fix.. about $20 delivered) and the noise is now quite low... comparable to ~75% of the amps I've mic'd while recording bands over the past 10 years.
Next weekend I'll be permanently mounting the transformer, and adding a humdinger. Then this damn amp can get the heck out of my house ;-)
Next weekend I'll be permanently mounting the transformer, and adding a humdinger. Then this damn amp can get the heck out of my house ;-)
Standalone transformer + humdinger trim-pot helped silence the amp. But then I played it for 10 minutes, until it heated up, and it jumped into a howling oscillation. I let it oscillate & chop-sticked every damn component on the 2 PCBs until I tapped the reverb pot & heard the sound change. I found a bad solder joint on that pot & re-flowed it. I've now played it for a full day, let it heat up real good, no problems. That said, as I was re-installing the front panel potentiometer nuts, little bits of the oscillation would return until the nuts were tightened down. As others on this thread have suggested, I think the design is a V1, and is on the hairy edge of unstable, w/ various ground loops just begging to howl.