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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. 
128x128johnread57

Showing 1 response by charles1dad

charles1dad's avatar
charles1dad
10,236 posts
 
To say that autobias is " no good ever" is hyperbole. I own 3 tube amplifiers, 2 are manual bias and one is autobias. All 3 are very fine amplifiers but the autobias amplifier is every bit as reliable (if not more so, 8.5  years of nearly daily use ) and the best sounding. No component or part is perfect and things occasionally need to be replaced or repaired, stuff happens. To universally denigrate autobias is silly in my opinion. Implementation as with all things involving audio is the overriding factor.
Charles
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