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FDP Forum / Fender Amps: Vintage (before 1985) / When a vacuum tube goes bad


USA / Sesame St.

Dec 18th, 2016 09:45 AM   Edit   Profile  

What causes the silver getter flashing on the top inside of the tube to turn powder white. Does it happen when air enters the tube?



Why do I keep fixing things that work?
Dec 18th, 2016 10:00 AM   Edit   Profile  

Correct. The tube developed a leak and is no longer any good.


USA / Sesame St.

Dec 18th, 2016 10:50 AM   Edit   Profile  

There's a clear slightly curved line etched in the glass above on the top of the tube that's about 3/8" long that I can feel with my fingernail. Feels almost like a crack in the glass. Looks to be in the area were the tension spring inside the tube shield makes contact with the tube.The tube is an original RCA 12AT7 tube from 68.

Moderator Emeritus
(with many stars)

NW Pennsylvania

Dec 18th, 2016 11:22 AM   Edit   Profile  

Time to replace it.


USA / Sesame St.

Dec 18th, 2016 11:27 AM   Edit   Profile  

Time to replace it. I agree with you, already been changed out with another. Lost my Reverb and found the driver tube wasted. All is fine now.

FDP Forum / Fender Amps: Vintage (before 1985) / When a vacuum tube goes bad

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