Quote:
Originally Posted by johnnycom
Hey Marty. I recently had some problems with my JCM900 Model 4100 Dual Reverb 100 watt head and we decided I had a bad tube. My head has Sovtec 5881 power amp tubes and I bought a matched quartet of Tung Sol 5881 tubes from Musicians Friend. They were a lot shorter than the originals but the tech thought they would be OK. He put them in and turned it on to bias them and they got real hot and now the head has no output at all. Could this have blown the PT? Are these the tubes you were referring to that we should stay away from?
Thanks.
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Well I have to say that a lot of Russian tubes are relabeled many different ways. The Sovtec's you had were probably 6L6GC tubes relabeled as 5881 and that's why they were taller. A 5881 is shorter than a 6L6, so there should be no problem with the size of the tube. What this sounds like is that your tech did not lower the bias pot before turning the amp on. When the amp was turned on, the bias value was so hot all four tubes red plated. If it took out your output tranny, that's too bad, but I guess it could. This looks like a situation where the tech needs to eat some time and parts because of his f**k up. Let me know how it turns out. BTW, the Tung-Sol tubes I was talking about up there ^^^ are preamp tubes. They have nothing to do with your problem.