Awhile back I had a bias pot go bad, and I lost my left channel. I replaced all the original 20k (measured value) pots with some higher quality 10k Czech pots (changing the resistors in the 1.2k slots to 5.1k, and 27k in the 22k slots as per a previous discussion here). While I was at it, I also upgraded all the resistors on the output tubes. I then powered up without issue. So far, so good.
Two problems, however:
First, I still don't have a left channel. Or possibly one that is very, very quiet. (Edited to add: I am getting some sound in the left channel, about half or 1/3 that in the right) Right channel works fine. I checked the plate voltage with the bias pots zeroed out, and I got 473v across the board at initial power on. That decreased as the delayed start approached, but with a variance in the left channel (466v) vs the right (460v). Not sure how to account for the difference, and if that is indicative of the problem?
At any rate, clearly the tubes are getting power. What could be the issue then with the left channel? Power but no signal? A preamp section issue...?
Second problem: with the new 10k bias pots I can't get the the tubes to bias properly. By my calculation, to bias the el34s to 70% at that plate voltage, the settings should be in the neighborhood of 37ma. The most I could get out of the new pots was around 22-25ma, cranked all the way. Not sure what the problem is. Need different value resistors?
Any help or suggestions as to proceed with diagnosis of the problem and/or potential fixes would much appreciated.
PS: I have eliminated all potential problems with cables, tubes, inputs, etc.