I think I got it. Detached enough wires on the turret board so that I could get under it and check connections. Sure enough, the wire on the underside of the post where the R20 and R23 v3a and v3b plate resistors meet was loose. It was in the eyelet but loose. Strengthened the connection as well as a couple other iffy looking ones. Put it all back together, checked voltages with the power tubes and preamp tubes out, then with the preamp tubes in and finally with the power tubes. All is in spec. The bias was rock solid, no up and down crap. Played through it for a bit, sounds normal. Still have the Shuguangs in it which I don't like. Tomorrow I'll play some more, if it holds I'll put in the KT66s, rebias and keep my eye on it.
I'm guessing probably when the amp was sitting upright in my cabinet that wire which was loose could potentially make enough of a connection to make the amp work, but over time if I moved the amp the symptoms of the bad connection would show up at random times. Which would explain why the amp would work for a couple weeks and then act up, then be normal in the techs shop.
Keeping my fingers crossed that the issue is resolved. Thanks again for the input everyone.
I'm a better HVAC tech than I am an amp tech but I can say that when there is that sort of irregular/intermittent behavior that it always 100% of the time comes down to an unstable connection.
Tweet
Comment