2. amps-preamps
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Do all tubes char inside when they die?

I have a Jolida 502B with Sovtek tubes, about 2-3 years old. I had a tube flare the other day (brightened and then dimmed), but didn't have noticeable effect so I kept it.

BUT, tonight a different tube flared bright red and stayed bright, bright red (all the metal in the tube, not just the standard spots)... the metal didn't cool until I manually shut the amp down. Scared the crap out of me (the top of the tube is blistered and inside is charred).

Is this normal? The tube doesn't sound horrible (I restarted the amp to do a sound check...probably stupidd thing to do).

Should I just replace the tubes or could this be an amp issue?

Thanks!
jc_audio
nsgarch's avatar
nsgarch
2,524 posts
 
I basically agree with Jeff, but as a precaution, it might be advisable to have the unit checked out to make sure that some passive component (like a bad resistor) is not causing tube failure.

If your tubes were all placed in service at the same time and have been working reliably for some while, it is unlikely (but possible I suppose) that one would just fail catastrophically all of a sudden by itself.
newbee
4,767 posts
 
Nsgarch, re your last sentence about the unlikelyhood of catastrophical failure in a well used/tested tube being unlikely. I guess I've been unlucky as this has not been my experience on several occsions.

But in all other respects I agree it could be something else especially in view of the poster's observations regarding another tube which also flared up and quieted down. I've a tube amp with an auto bias circuit and had a tube's plate start to glow red. I changed out the tube but there was no change in the red plate syndrome. Sent it back to mfg'r who adjusted bias circuit - all is well now with original tubes in place.
jc_audio OP
1 posts
 
Thanks folks for the heads up! I'll get the unit checked out just in case, but I'm glad to hear this isn't completely out of the ordinary...
nsgarch's avatar
nsgarch
2,524 posts
 
Newbee, I guess I should have qualified that comment.

I didn't mean that if a tube has been behaving it should never explode! And if it does it could just be random failure, but I just meant I'd look elsewhere too, especially if it's been giving good service and isn't at the end of its (sonic) life yet.
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