Topmusicanswers
It is either your power cord has gone bad, or the jack for that power cord gone bad. Or both. Either way, try to change your power chord and see if there's a significant difference. Or try this: wiggle your power chord when your amp is turned on, with guitar plugged in.
Why does my amp fade in and out?
Generally, tube amp fade out, is caused by bad power tubes, but since you changed them, I suspect a bad plate or cathode capacitor. When it gets hot, it physically changes shape and goes bad. They are generally in close proximity to the tubes. It may also be a bad or weak socket.
How do I know if my guitar amp is blown?
The most common aural indication of a blown speaker is an unpleasant buzzing or scratching sound, by itself or roughly at the pitch of the note the speaker is attempting to reproduce. Or there could be no sound at all.
