05-30-2018, 05:03 PM
This is resolved. As with everything in this amp, it seems, the issue was complex. I tested several grounding points for the intensity pot, and found that the situation was much improved by grounding it to the board on the same ground circuit that the tremolo uses. With this ground, I still had hum attenuated by the intensity pot, but I only had that from 0-2. it was previously present at all ranges (0-10).
OK, so then there was the question was where all the current coming was from that was driving the noise? I figured it needed to be one of the 6SN7s. I eventually isolated it to V2, and found a tube that worked in that spot that wasn't microphonic (so many of mine are), and which eliminated the hum. Now, the interesting thing is that by swapping out V2 the trem also improved (less noise, stronger trem). I guess V2 was pulling so much current that V1 was under voltage; likewise, you may remember that activating the trem reduced the hum. I guess the additional current for the trem starved V2 to the point of reducing the audible hum. Dunno. Anyway, done.
I can't say that the amp is super quiet, but I think it's as good as it's going to get. It wouldn't be noticeable if I wasn't in a small room. The amp now sounds simply awesome. I had forgotten just how much I like it. The trem and reverb both go to "way too much", and it's lovely with both turned off. If you don't already have one of these, you really should get one.
OK, so then there was the question was where all the current coming was from that was driving the noise? I figured it needed to be one of the 6SN7s. I eventually isolated it to V2, and found a tube that worked in that spot that wasn't microphonic (so many of mine are), and which eliminated the hum. Now, the interesting thing is that by swapping out V2 the trem also improved (less noise, stronger trem). I guess V2 was pulling so much current that V1 was under voltage; likewise, you may remember that activating the trem reduced the hum. I guess the additional current for the trem starved V2 to the point of reducing the audible hum. Dunno. Anyway, done.
I can't say that the amp is super quiet, but I think it's as good as it's going to get. It wouldn't be noticeable if I wasn't in a small room. The amp now sounds simply awesome. I had forgotten just how much I like it. The trem and reverb both go to "way too much", and it's lovely with both turned off. If you don't already have one of these, you really should get one.