Marshall Valvestate VS100 combo cuts out

[busydoingnothing]

Hey guys, my amp is buggin on me. After about 45 minutes of practice or so, it just cuts out. I don't get any sound. I then turn it off, get a kind of loud popping sound, wait a few seconds, then turn it back on and I have sound. Sometimes it'll cut out again after that.

I took it apart and checked the solder joints and they're all good. In the past, I had a cap that would get a cold joint that I would have to re-solder again. I recently had to re-solder the input jack because a couple joints were loose and it would cut out unless I put pressure on the cable.

What's it sound like? Bad tube?

[sumgai]

bdn,

You don't have tubes in there, except for the one in the gain circuit. That isn't causing your issue.

Whenever I find a "popping sound from the speaker" problem, I look to the capacitor(s) in the output circuit, between the two (or more) output transistors and the speaker's negative lead, or else the circuit ground itself. In both cases, a capacitor that is heating up can change value enough to shut off the output, and when it cools back down, which doesn't take long, the output is restored.

Popping sounds are always the result of a capacitor discharging its stored charge of current. Many more modern circuits (like your Marshall) have resistors to slowly discharge the cap, and bleed of the stored charge in such a way that you should never hear it out of the speaker. If you do hear it, suspect the cap(s) first, then the resistor(s) around it/them. As with other parts of your circuit board, re-heating the solder joints may be all that's needed here, so start with that.

HTH



sumgai