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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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Showing 1 response by atmasphere

atmasphere's avatar
atmasphere
11,640 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.
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