Amp keeps blowing reverb driver chips

[TimmyP1955]

Thread tangent: What's with the abnormally large grid stoppers on the outputs?

[wizard333]

Thread tangent: What's with the abnormally large grid stoppers on the outputs?

You mean R69/72? Yeah they are abnormally large, I'd have to assume he was trying to prevent some high end oscillation issues there. I have a mod I do on these amps that turns them from cold and meh to something that can do anything from Metallica to Larry Carlton; Dumble Marshall Mesa are all in there. With a collection of Vintage amps and modern amps I've modded, Friedmans, etc, these are still my reference amp post mod because there is no sound in my head I cannot get from them. With all the changes I do, I've never changed those grid stoppers. I assume they are what they are for some sane and functional reason, but can't swear to it. I don't hear them doing anything bad, and I don't want to take a chance on introducing an oscillation issue by going to a more traditional value.

Thanks to everyone that helped out! Note to self, which I've made before but forget: There is as much variation in those little silicon things of a certain type as there are in tubes of a certain type. I never assume non-adjustable-fixed-bias tubes are correctly biased, I shouldn't assume it with transistors either.