2. amps-preamps
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Power tubes glowing?

I've been listening to some stuff at pretty high volumes lately- enough to make your ears ring- and the last couple of nights, the ceramic insulators on my 845B tubes actually glow orange. You can't see it when it's daylight, or when the lights are on, but when it's dark, and I power everything down, the ceramic insulation is glowing orange hot. I know these tubes can run up to 200 degrees F, but should the insulation glow? Doesn't sound like it's clipping or overdriving, and I biased the tubes about a month ago. Something to worry about? Will it shorten tube life? Or perhaps I should re-bias the power tubes? Any ideas? Or am I fretting about nothing here?
afc
7 responses Add your response
afc OP
141 posts
 
LOL Viridian. You crack me up. I'm not far behind you at "almost" 49, and my hearing is dinged up from skeet shooting as a youngster without ear protection. Loud music and concerts haven't helped. Left ear is definitely deficient.

Ed- what if the plate does glow? Do what? Now, it's just the insulators, and it's both tubes. They have perhaps 100 hours on them. Don't want to blow them up. Will re-bias tonight.
Post removed 
afc OP
141 posts
 
My hearing is already compromised. I could probably play a circa 1970's radio and not notice the difference.
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clio09
3,355 posts
 
Try re-biasing the tubes. If they won't re-bias properly or if the orange glow continues I'd replace the tube. You don't want to have a tube explode on you.
xagwell
132 posts
 
I've shattered a few EL 34's, but orange color in my experience has usually meant biasing. The orange glow occurred just before the tube exploded. It ca also mean a start of a bad tube.
ed_sawyer
588 posts
 
I wouldn't worry about it too much. Usually if the plate (the graphite part in an 845B) is glowing, that might be an issue. They can run well higher than 200F. More like 500+F measured at the envelope (so even more inside.)

-Ed
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