Power Tube SCREAMS Like a Monkey! - Fender Twin Reverb Service

This is a later 1978 ultra-linear (UL) 135W Silverface Fender Twin Reverb that has extensive servicing and mods done before me, but customer complaining of noise and "glassiness" in the tone. We'll open it up and look at the mods done, and we'll eventually diagnose the problem down to bad output tubes, listen to one of them squeal like a tortured primate on command, then change tubes and rebias.
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