Strange clicking noise

[aro]

I bought a used 2204 clone and it seems to be a great amp, with one little exception.

What happens is that it has a clicking sound when I play it. I thought initially it was coming from the OT, but that’s unlikely.

The click doesn’t come through the speakers. It’s audible only when I play it through an attenuator with the attenuator volume all the way down. Also, it can be heard only with the chassis out of the box.

When I play single notes slowly it can be heard after every single note, maybe half a second after the note was played. I’m quite certain it comes from the half of the board/chassis with V1, 2 and 3, not the power section. Maybe more towards V1, but it’s hard to pinpoint exactly. Also, it doesn’t seem to come from the “top” of the chassis, with all the transformers and tubes, but rather from inside the chassis.
I wouldn’t worry about it but I’m afraid it might become a more serious problem later on.

[PRR]

When I was running a big SE amp on test-tone into dummy load, some power tubes would creak as the tube shifted from 36W idle to 20W full-output dissipation.

[plexi50]

Re check your bias and monitor it for stability. It will normally fluxuate as you play. You might have a problem with the bias caps if there is a slow return to idle

Just an idea /

[aro]

The bias recovers fast. I tried different power and preamp tubes and no luck... I'm just going to start playing it a lot at practice. It if blows up at least have it do so during practice rather than live.