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This is a KT77 that looked like it might have gotten a bit warm. This is the first time I have seen the glass melt on a tube. I was listening, sounded fine, then the music stopped. It may be a bit hard to see in the picture, glass melted inward and cracked, is this common?
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I've never experienced a meltdown like this with cathode bias.
A prime example of where fixed bias is used and a tube ran away. Hopefully your output transformer survived.
AM
nt
I had to laugh when I read that. It is good to hear from you, hope all is well.
Thanks Fred, same.
it is not normal and it's obvious that the tube lost its bias. A poor contact in the socket is likely since it is just the one tube. Red hot plate for ? minutes. The reissue GL's are well made tubes.
I am assuming of course that all was good before.
I might check some of the resistors and Caps adjacent (but in the circuit) for the power tubes - and of course its mate - assuming a PP set-up
I had an old scott run away one time when the cathode resistor failed.....
took out the OPT also...
Happy Listening
I appreciate the suggestions. I posted it as a curiosity. My first job was fixing TV's and HiFi's, when most were tubes. And many years later I still fool around with tube equipment, and this was the first time I had ever seen the glass melt on a tube.
Saw a pic of an SVT equipped with 6550's. All of them pulled the glass onto the plate. two still had shiny getters. These were the small Sylvania 6550...so perhaps a concentrated hot spot was possible.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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