Amp's tone changes when hot

[R.G.]

For the initial tests, you have the right idea - just prop the fan up in approximately the place it will go and see that happens.

Getting the tube heat out of the box will also lower the temps on the components, and removing stagnant air will do even more for them.

[d95err]

Also, within a short amount of time at medium to loud volume levels.... your frickin' ears can start to shut down, become slightly fatigued and change your perception of tone.

That would be my prime suspect too. First thing I would check is:
- If you record the amp when it's just been turned on, then again after playing 20-30 minues. Is there an audible difference?
- If you turn the amp on, have someone else play it for 20-30 minutes when you're in another room. Does it still change tone?

[daz]

GOT IT !!! Bad winged C ! Guess this speaks to the bad QC i been reading with winged C's during the last year or so. I have a small stash but i don't know what i'll be doing when they are gone, and now i worry about buying more to stash up before they are all gone since the ones out there now are possibly unreliable. Nothing sounds the same to me, and i've tried almost all current production.

Anyways, i found out it was a bad tube because i was checking the bias and playing the amp and it still doesn't seem right even cold ever since that nite. I tapped the tubes and when i tapped one it arced and took out the mains fuse ! Put in another winged C and biased them and the tone is back to normal. Makes me wonder about the rest i have because many are newer ones. While on the subject, one of the few i have not tried of the current production (maybe THE only one) are the russian mullard reissues. anyone compared them to the winged C's?

[R.G.]

It's funny - I even tell people over and over that the first thing you do in finding out what's wrong with a tube amp is to sub in known-good tubes. And I didn't even dredge this up. I probably assumed at some unconscious level that and old hand like you had already done it.

Good catch!

[daz]

It's funny - I even tell people over and over that the first thing you do in finding out what's wrong with a tube amp is to sub in known-good tubes. And I didn't even dredge this up. I probably assumed at some unconscious level that and old hand like you had already done it.

Good catch!

I usually do too, but the type of issue just didn't seem like it would be a tube. I'm used to tubes just going out in a blaze of glory or sounding obviously wrong immediately. But the way it seemed to take a while for the amp to heat up just screamed heat related to me. But like you tubes are usually my 1st thought. I also had a marshall that did the same thing even over the course of years of use with many different tubes.