77 twin reverb

[Rhodesplyr]

To amplify pdf64's comment, one thing I've run into twice over the last year is an amp where the initial problem causing the tubes to red-plate has been fixed, but it continues to happen because the tubes were damaged. The control grid has a coating that's supposed to prevent electron emission by the control grid, but if that coating gets blown off, the amp can do exactly what's being described. In both cases I dealt with, the amp ran OK for about 15 minutes and then went out of control That time delay was the time it took for the internals of the tube to get hot enough to go into thermal runaway. One of these was a Fender Super Reverb with STR387s in it. Once the control grid starts to emit electrons, you have current flow that will throw the bias off, and it's a positive feedback mechanism: the hotter things get, the worse grid emission becomes. You can watch it on a meter; you'll see a little bias creep, and then it will accelerate.

[majwild1]

Well I don't have time to take it to the cities to have it repaired, if anyone knows of a good amp tech in the saint cloud,mn area let me know. I think I'm just going to have them go through it.

[Enzo]

Go to fender.com and look in the service center finder. Fender repair shops are not rare.

And ANY competent amp repair tech can handle this. Working of Fender amps is no different from working on other brands. A 6L6 is a 6L6 wherever it is used.