Did you switch the tubes in the left channel with the right channel tubes to eliminate the possibility of the tubes being the problem?
I think a "crack" or "clack" -type sound can also indicate an A/C 'leak' within the amp, though I'm not sure if that would present itself in only one channel.
I had a Jolida 502A years ago that developed that exact problem - that same "clack!" followed by the volume-fading-out-then-fading-back-in phenomenon. I took it back to the dealer, and, of course, they couldn't get it to reproduce the problem there in the store (even leaving it on for days at a time). I really loved the sound of that Jolida otherwise (it was my first foray into the world of tubes), but had to get rid of it when I was unable to get to the bottom of what was causing that noise.
I think a "crack" or "clack" -type sound can also indicate an A/C 'leak' within the amp, though I'm not sure if that would present itself in only one channel.
I had a Jolida 502A years ago that developed that exact problem - that same "clack!" followed by the volume-fading-out-then-fading-back-in phenomenon. I took it back to the dealer, and, of course, they couldn't get it to reproduce the problem there in the store (even leaving it on for days at a time). I really loved the sound of that Jolida otherwise (it was my first foray into the world of tubes), but had to get rid of it when I was unable to get to the bottom of what was causing that noise.
