JJ KT-77 failure

greiswig · Post by **greiswig** » Mon Feb 25, 2008 8:13 pm

Hi,

I have a pair of JJ KT-77s, which suddenly developed an issue. Plate voltages are 430, tubes were biased at the time at about 35ma.

The amp I was working on with these in it *may* have had a short in the speaker cable for a moment. The sound cut out, and fiddling with the speaker cable "fixed" the issue enough for me to R&R the cable. No more cutting out.

But now, there is a low noise coming from the power section, similar to the white noise you get when you put a phonograph needle on the blank strip at the beginning of an LP. The noise goes away if I replace the tubes with something else.

What kinds of things cause this noise in a tube? Could a shorted cable have caused the tube to fail?

Thanks!