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tube/bias adjustment problem?

Turned off my system today at the end of a listening session and heard a troubling rumbling static noise in my speakers. Historically this has meant the end is near for one or more of the KT88 tubes my VAC PA80/80 amp employs. So I put in some old tubes to bide me over until I could order some new ones. With the system still off I turned the bias adjustment screws for all four tubes counter-clockwise. I turned the system back on and slowly turned the first screw clockwise and waited to see the LED indicator light turn from green to red, at which point I would normally slowly back off to restore green. Unfortunately, I was unable to get red even after turning the screw all the way clockwise. I backed off on that first screw and went to the second. Again, couldn't see any red, even after going all the way clockwise. Too worried to test the last two tubes, I just shut the system off and pulled the plug.

Is anyone here knowledgeable as to whether this indicates a failure of the bias adjustment on the amp unit? Or is it possible my old set of interim tubes have all suddenly failed at the same time?

can anyone recommend a good tube repair shop in the Rochester, NY area? I used to go to Kelsey-Pape, but sadly they shut their doors a few years back and I haven't had the occasion to go to a repair shop in the time since.

Thanks in advance for any advice you can offer.


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Topic - tube/bias adjustment problem? - coffeequeen 15:37:00 03/11/07 (3)


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