I got a used Jolida SJ-502a last week. After I replaced a 12at7 damaged in shipment, it sounded fine for a couple of days. Then I changed cables, and accidentally left the right channel on without a speaker load for a few seconds. Since then, I've had problems with the amp flickering on and off for several minutes after powerup, triggering relays that shut the sound off and sometimes flickering quickly enough that a popping sound gets through to the speakers.
Characteristics:
not affected by volume knob
too brief to tell if it's just one channel
can't tell if it's coming from the tubes
tends to happen a lot for the first minute after powerup, then very seldom
popping sound is fairly soft
I don't know if the Jolida has relays on each channel. I haven't blown any fuses. Bias tests as normal. After 30 minutes I can listen to music with no apparent problems except a click once every hour or two.
While I've found long lists of things that could be wrong, they are usually described as getting worse the longer the amp stays on.
Could anybody help me narrow down which parts might be damaged or arced?
