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My Dynaco MK IV amps BOTH do the same thing from time to time.
One of the tubes glows red hot. Have to shut it off, and then later when I run it its fine. Then within a week or two or less same thinig happens. I dont know much but I do bias the amps and everything will show fine them it will happen again.
Only pattern I notice is it seems to do it when, the amp is firts turned on and just setting for a little bit. Not exclusive to that but is a pattern. I dont know a lot about repair had someone work on these amps a while back because of this problem and replaces a lot of caps etc. but still it occurs.
Any help much appreciated.Thanks in advance, when it plays it sounds wonderful but who wants to be nervouse about tubes over heating. I mean one will glow orange hot.
Follow Ups:
The single most likely culprit is the grid bias being intermittent for that tube. Like Mike Samra said, probably something as simple as a bad contact or dirty/failing pot.
It sounds as tho you may have a bad set of output tubes that develop leakage after being on for a while or you may have dirty tube sockets or bias pots or both. Are you using tubes like the early JJ KT77 or some el34s with small pins? If you are they may not be making good connection with the tube sockets and this will cause a runaway output tube on occasion.
Thanks Mike I will clean pots and the sockets today and see how that works out. Not the tubes have tried several differant sets all eventually do the same thing, on both amps with differant tubes at dif times, always just one tube on one amp but which tube and amp vary each time.
thanks for your advice,
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