So,
After three separate Skype sessions with Brian leading me through test procedures as well as some voltage meter checks on my own, putting a sine wave through the amp and taking a variety of measurements on the 300 B tubes, here's what we know:
We have verified that one suspect  that the volume pot might have been wired incorrectly (it's actually a somewhat complicated procedure involving six separate connections)  is fine. The volume pot wiring is good.
Most of the AC and DC voltages look perfect, even better than usual.
But there is some odd behavior with a few of the AC voltages vis-Ã -vis how things react when the volume pot is raised or lowered.
We also discovered that I have four ceramic capacitors soldered in the wrong position on the driver board, although these are not in the signal path and would not be causing the symptoms we've been hearing. (Brian is going to send me a set of replacement capacitors.)
At this point, Brian is pretty convinced that there is a problem with the driver board passing along a clipped or distorted signal. So we're going to do another Skype session and he will lead me through a step-by-step series of voltage checks on each stage of the driver board.
We should be getting there soon!
After three separate Skype sessions with Brian leading me through test procedures as well as some voltage meter checks on my own, putting a sine wave through the amp and taking a variety of measurements on the 300 B tubes, here's what we know:
We have verified that one suspect  that the volume pot might have been wired incorrectly (it's actually a somewhat complicated procedure involving six separate connections)  is fine. The volume pot wiring is good.
Most of the AC and DC voltages look perfect, even better than usual.
But there is some odd behavior with a few of the AC voltages vis-Ã -vis how things react when the volume pot is raised or lowered.
We also discovered that I have four ceramic capacitors soldered in the wrong position on the driver board, although these are not in the signal path and would not be causing the symptoms we've been hearing. (Brian is going to send me a set of replacement capacitors.)
At this point, Brian is pretty convinced that there is a problem with the driver board passing along a clipped or distorted signal. So we're going to do another Skype session and he will lead me through a step-by-step series of voltage checks on each stage of the driver board.
We should be getting there soon!