trinityamps.com

18w Plexi/Brown MKII built from a kit.

It only happens when I have the volume up past 4 or 5 on the high input of either channel, and only when I playing certain notes or chords with a hard attack. I suspect it might happen if I had it loud enough on the lo inputs as well. I can't say which notes or chords cause it to happen as it seems to change depending on the volume. It's like it exceeds some kind of threshold and the sound breaks apart and crackles badly.

Could it be a bad solder connection? Bad tube? Other? Any advice on how to narrow in on the problem?

Thanks

solder joints are the first thing I'd check.
I've had that many times.. often with either big hard hit chords or only on certain notes..
I chased my champ noise from F to C just a couple days ago.

sometimes you can even pull on a wire or component, it's firm and seated, yet the joint is still bad.
Sometimes you can turn the wire in the joint.. or you can wiggle a wire and see the end through hole moves.

Reflow solder.

Just be methodical and patient and I bet you find something hinky.
You should just say.. though it's hard.. I blew the soldering, so I'll redo it all.
don't forget to unplug, watch out for filter caps, turn pots all to zero.

Thanks Twang. When I first started it up I had a problem that I traced to a bad solder joint on one of the volume pots, so I think your advice is good. I'll go back and check all the solder connections and report back.