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Non-match power tubes

24.205.20.241

Steve,

Pardon my Q---but what is the mechanism behind an unmatched pair of push-pull tubes leading to one tube going ballistic?

The only time I've had this problem is when one of the pair has a short in it. This tube basically sucks a ton of current from the PS---which usually ends up taking out its partner. And sometimes the PS/PT.

I just redid an amp with brand new JJ E34L. They were supposedly matched. One had a Gm of 5600. The other 8800. The amp sounded REAL lousy. But, there were no signs of thermal distress. And this amp is Class "A" cathode biased with a bypass cap and resistor on each tube.

Usually, when amps get old and haven't been serviced---the Gm of the p-p pair are way off. The amp sounds weak or has oddball clipping tones---but I haven't seen one blow up.

Honest Q---do you have any personal examples of this mis-match leading to catastrophe? I'd be interested.

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