have i diagnosed my hum?


Tube newbie here, looking for a bit of common sense in diagnosing a problem.

I have a stock Jolida 302brc that is producing an audible hum at the speakers, with or without any input applied, and regardless of volume level. I've sorted out the grounding issues, and the amp produces the same hum (again, at the speakers, not from the chassis) regardless of where or how it's plugged in. It's very audible from the listening position.

Resolution Audio here in Seattle was kind enough to loan me a pair of EL34 tubes to swap out for a pair of mine, thinking that I've got one or more tubes that are bad. When I made this change, the amp sounded horrible playing music (like a damaged driver; a very 'torn' and distorted sound), but the hum disappeared completely.

I'm assuming that this means that A) yeah, I've got one or several bad output tubes, and that B) the loaner tubes I used were way out of bias during this brief test.

Does replacing my driver tubes seem like a reasonable next step?

Thanks in advance for any comments or advice.
soundgasm

Showing 1 response by 4est

Is there a reason why you did not bias the amp for the new tubes? It would seem that is the plase to start, then as Rleff said, swap them one at a time. Do any of the tubes glow red at the plates as opposed to the heaters?