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Gear / Technical Help => Playback Forum => Topic started by: Tim on July 25, 2005, 08:14:26 PM

Title: whoah... just had a tube go bad
Post by: Tim on July 25, 2005, 08:14:26 PM
whole thing was glowing BRIGHT orange

yikes, I thought it was going to explode

btw - this was one of my svetlana el34's
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 25, 2005, 08:51:57 PM
luckily I have a spare set of tubes....

I noticed that my left channel was operating at a significantly lower volume so I powered everything down and switched one tube on each side, that's when they bright glowig occured...

maybe the bias was just really bad?
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 25, 2005, 08:52:51 PM
you know I just had a thought, I was listening to a Rat Dog tape... maybe my amp just doesn't like Bobby? :P
Title: Re: whoah... just had a tube go bad
Post by: cheshirecat on July 26, 2005, 02:29:03 PM
Try swapping the tube back then swapping the other 2 EL-34s to see if you have the same behavior, and also right channel pair to left... Depending on how they're biased (pairs or individually) they may just need to be rebiased.  It could actually be not the glowing tube but its complement not drawing enough power...
Title: Re: whoah... just had a tube go bad
Post by: macdaddy on July 26, 2005, 02:33:41 PM
Quote
It could actually be not the glowing tube but its complement not drawing enough power...

beat me 2 it. +t
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 26, 2005, 02:34:09 PM
it was a bad bias... the plate was glowing, but it scared the crap out of me!

but really I think one of my 12au7's is going bad... one channel is louder than the other. I'm just getting ready to figure out which one it is

edit to add: my tubes are individually biased
Title: Re: whoah... just had a tube go bad
Post by: cheshirecat on July 26, 2005, 02:42:02 PM
sytematically swap them from left channel to right if you don't have a tube tester.  That will let you isolate the bad tube.
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 26, 2005, 02:43:43 PM
that's what I'm doing :)
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 26, 2005, 08:11:30 PM
found the offending tube, luckily these JJ ECC82's (that sound so amazing in my amp) are only about $10/piece....

I tried some RCA Clear Tops that Nick Culbreth has (thanks again Nick!) and found the two to be almost indistinguishable (even in blind comps), the RCA's are $35/piece.. lucky me :)
Title: Re: whoah... just had a tube go bad
Post by: BobW on July 26, 2005, 09:58:43 PM
Quote from: Tim on July 25, 2005, 08:51:57 PM
luckily I have a spare set of tubes....

I noticed that my left channel was operating at a significantly lower volume so I powered everything down and switched one tube on each side, that's when they bright glowig occured...

maybe the bias was just really bad?

Yes, check bias !
Plate was glowing due to excessive current draw.
Swap speakers for a few days.  (switch left for right)
Check cables.
Tube may not be dead.......

Good luck, be careful, think it through and move slowly.
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 26, 2005, 10:12:40 PM
I've swapped literally every component around

I used to take apart and put back together sizable PA systems, so I know how to trace a problem :P
Title: Re: whoah... just had a tube go bad
Post by: BobW on July 31, 2005, 10:00:57 PM
Quote from: Tim on July 26, 2005, 10:12:40 PM
I've swapped literally every component around

I used to take apart and put back together sizable PA systems, so I know how to trace a problem :P

Sorry, it's hard to remember who's had which experiences here on the board.

Was it the tube or a shorted output ?
Title: Re: whoah... just had a tube go bad
Post by: Tim on July 31, 2005, 11:14:41 PM
tube :)
Title: Re: whoah... just had a tube go bad
Post by: Charlies on July 31, 2005, 11:41:01 PM
Quote from: Tim on July 25, 2005, 08:52:51 PM
you know I just had a thought, I was listening to a Rat Dog tape... maybe my amp just doesn't like Bobby? :P

T for listening to Ratdog!!  ;D