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Autobiasing tube amp failure

The smell of electronic burning alerted my wife and I. I turned the amp off and removed the power chord. I opened the casing and couldn’t see anything wrong. But there was definitely a strong burnt electronic smell. Later investigation showed that one of tubes had gone way out of bias and caused one of the resistors to be overloaded. 

My question is how can this be prevented in future? Autobias means no way of reviewing the tube settings and performance.

The tubes and amp are less than 150 hours into their life. 
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cleeds
5,642 posts
 
Occasional tube failure is inherent in vacuum tube components.
ebm
9,311 posts
 
This happens with tube amps i had CJ Premier 5,ARC D150 etc i now use a solid state amp as i hated always getting them fixed.Consider yourself lucky as a few times they blew out my Tweeters.
facten
2,723 posts
 
You state that the amp only has 150 hours on it, was it purchased new? If so, have you contacted the mfg? 
atmasphere's avatar
atmasphere
11,569 posts
 
Consider yourself lucky as a few times they blew out my Tweeters.
A tube failure won't blow out a tweeter! Tweeters fail because the amp being used is underpowered and is making too much distortion when driven too hard.

My question is how can this be prevented in future? Autobias means no way of reviewing the tube settings and performance.
Autobias assumes that the tubes are OK- it usually can't do much about a tube that is arcing or shorted. If you are concerned about this, I would consider having the amp modified with fuses in series with the cathodes of the tubes to prevent them from damaging the amp.
audioman58's avatar
audioman58
3,832 posts
 
For Tube Amplifiers  Auto bias No Good Ever , for it adds extra circuitry and resistors. It average each channel .
Manual bias far better  you adjust  each tube individually 
And when a tube does go, just review  the new tube,  recheck others and done .it takes may be s minute per tube some compsnies  still want you to use a meter way out dated.,  I had my own Simpson meters added and switch per channel  ,seperste volt meter is primitive and s pain in the ass.
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