2. amps-preamps
  3. 1276573000

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 detredwings

detredwings
162 posts
 
Soundgam,

How old is your amp and approximately how many hours on the tubes? Also did you try to bias the tubes after you put them in? You can also try to change out the 12ax7 and 12at7's if you have an extra set or at least pull them out and clean them and put them back in or reverse sides with them. Sometimes dirty pins will cause odd problems.

Good luck
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