Mesa Quad problem, microphonic tube?

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Bottle Rocket
Posts: 11
Joined: Fri Apr 24, 2020 5:04 am

Mesa Quad problem, microphonic tube?

Post by Mr.Buu » Mon Jun 14, 2021 1:22 pm

Ive had this issue within the last week, whenver I turn up Master and Lead Master on Channel 1 Lead i get an incredibly high pitched squeal, Ive never had this issue before.

Im guessing its a microphonc tube? I turned off the sound at the speakers, and when I cranked the knbos in question the whistling was actually audible from the preamp out loud, despite it not outputting any sound from the speakers. I did the old tap test with a pencil whilst the amp was on but with no guitar input, but none of the tubes made a sound so Im not 100% certain which tube to replace.

Im guessing I should repace V23 tube from below schematic, as thats for lead 1 which im having issues on? ... -quad5.gif

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