Crackling during warm-up?

[Will]

In that cheapo halfstack my friend gave me - it's a hybrid, but the 12AX7 preamp doesn't do much. It has an LED behind it to simulate "glow".

During the first 2-3 minutes it's on, after the tube warms up, I get a pretty prominent crackling noise on the low notes and the volume fades in and out. In goes away after a few minutes and then the amp works fine. I get it if I bypass the preamp and plug straight into the effect return as well.

Anything to bother fixing? It was stored in a garage for several years, so I got the idea the filter caps on the power supply might be bad from not getting used. Other ideas?

[filtercap]

Dirty tewb pins and/or socket contacts? That doesn't explain why the crackle would only be at a particular time, but the dirty-pins syndrome does cause crackle that suddenly goes away and then comes back just as suddenly.

[Will]

Hmmmm... I know the board sat exposed for a while with nothing in the socket. I'll clean those out a bit and see where I'm at.

Thanks!

[Dogma Hollow]

In that cheapo halfstack my friend gave me - it's a hybrid, but the 12AX7 preamp doesn't do much. It has an LED behind it to simulate "glow".

During the first 2-3 minutes it's on, after the tube warms up, I get a pretty prominent crackling noise on the low notes and the volume fades in and out. In goes away after a few minutes and then the amp works fine. I get it if I bypass the preamp and plug straight into the effect return as well.

Anything to bother fixing? It was stored in a garage for several years, so I got the idea the filter caps on the power supply might be bad from not getting used. Other ideas?

I had a similar issue with my Hot Rod DeVille after I put new tubes in it. I just let it warm up on standby for a few minutes and it doesn't have the problem anymore. I could see it being loose contacts though. If they're just slightly loose when cold, the heat from the tubes might be expanding the metal enough that it makes good contact once it's hot. Just a theory though.