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Help troubleshooting amp

Hi,
When I turned the system on this morning in anticipation of a long holdiay of music there was no signal in my right channel. I first checked all connections which were fine and then I subbed in a pair of replacement tubes for the right side of my preamp, still only on channel. I then switched my attention to my amp, I switched both pairs of 6550's from left to right. Now no signal in either channel! This leads me to beleive that the trouble rests with the amp. I'm going to try switching 6550's back again but one at a time to see if I at least get the left channel back. Regardless I'm pretty sure it's a tube issue but if anyone else has any ideas I'm listening. Why do these things only happen on weekends and holidays?
128x128jond
jea48
4,321 posts
 
>>"I switched both pairs of 6550's from left to right. Now no signal in either channel!"<<
>>"This leads me to beleive that the trouble rests with the amp."<<
>>>>>>>>>>

Just a guess, a bad shorted 6550 tube. The bad tube may have damaged something in the right channel. Installing the bad tube in the left channel may have caused damage there as well.

Post a thread on Audio Asylum on their tube forum and ask your question.
http://www.audioasylum.com/audio/tubes/bbs.html
scifi's avatar
scifi
67 posts
 
I had the same problem with my VTL MB450's. A bad tube blew the main output fuse on one of the amps but the tubes themselves still lit up because there was a small amount of current going through them. The fact that there was current going through them mislead me to thinking that the problem was not the tubes.

I would agree with Jea48 that a bad tube on the right side when switched to the left side blew a fuse on the left side as well.

I would check the fuses (use a volt meter) on this amp to see if indeed they are blown. If they are, you need to replace the fuses and the tubes before proceeding any farther.

Scifi
ecclectique
509 posts
 
Hi Jond. Sounds to me like a bad tube[shorted] took out the cathode resistors in one channel and when you swapped them to the other channel, the same bad tube or tubes took out the cathode resistors in the other channel as well.If you have a tube tester, It would be a good idea to test all these tubes to ascertain what tube/tubes are shorted before putting them back in. Is your amplifier a self biasing circuit or can you bias each tube idividually?
kgturner's avatar
kgturner
663 posts
 
i'm sure you already have, but check the fuses on your amp. you probably have a bad 6550 as mentioned which caused your fuses to blow. good luck.
jond's avatar
jond OP
5,694 posts
 
Well guys I looked at the fuse and it looks fine. I don't know how to test it. I'm afraid that Ecclectique is right and a bad tube took down some resistors or something like that. I guess tomorrow I'll take it over to Deja Vu Audio and see if Vu's tech can take a look at it. What a bummer! Anyway thanks for the responses everyone, I'll let you know how it turns out.
Cheers,
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