I gave said amp to my son for graduation. I've noticed after it's been playing for a while I heard a weird sound. Tracked it down to the amp becoming very microphonic, and was causing feed back into the speaker. If I tapped the EL84's, the feed back would go away, but the tubes were VERY microphonic.
Appears the JJ El84's are quite microphonic. I thinking of replacing these. Any suggestions?