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I have a Jolida 1000A with 8 EL34 tubes that I bought used about two months ago. I just replaced the tubes and I'm able to bias 5 of them fine, but nothing happens when turning the appropiate adjustment on the other 3. Is it odd that 3 would happen to be bad? Any suggestions on how I should proceed?
I once bought a five pack of new EL84 tubes and, of the five of them, three of them actually worked. Happily, these were new tubes and the vendor was a standup guy, so I was able to get replacement tubes. With used tubes you really don't know. It probably isn't the guy who sold them to you. You can never know which package looks like a bowling ball to some shipper; or looks like the bowling pin; or gets carried by the horse with three legs.
I think in my case there's an actual problem with the amp because if I switch “good” tubes to the “bad” sockets I get the same results. Likewise the "bad" tubes begin to work great on the "good" sockets.
I called Jolida, and much to my surprise, they said it was still under warranty and so I sent it back to them for repair. This is a unit I bought used, so I was surprised to learn it was less than 1.5 years old.
It is odd but not impossible.Swtich the tubes around with the tubes you cant bias with the ones you can bias and see what happens.Bias is pretty straight forward but what can happen and i have seen this more than once where you have circuit board mounted tube sockets, and when you take tubes in and out you break or weaken connections and you need to just resolder them many times.I would do this anyway becuase its so easy to do.Take your bottom off the amp and just touch up the connections where they dont look so good and especially on pin 3 of the el34s.
I meant to say all the pins on the sockets but especially pin 5 where the bias comes in at becuase im sure its negative biased.
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