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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
xagwell
131 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.
clio09
3,346 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.
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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