Hoping you can confirm what I'm thinking...
Mesa Boogie Bass 400+ on the bench, with one DOZEN 6L6GCs in push-pull. On one socket, the grid and screen resistors are burned open. But when I pulled the tube and measured pin-to-pin resistances, there are no shorts.
Can I assume the failure happens only at high voltage, and that elements inside the envelope did not fuse together, so it reads normally at low voltage?
Power tube failure modes
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Power tube failure modes
I build and repair tube amps. http://amps.monkeymatic.com
- JazzGuitarGimp
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Re: Power tube failure modes
Your assertion sounds plausible, but I am no expert. Have you looked at both sides of the socket as well as the base of the tube for carbon tracks? Also, if you have a tube tester, checking for shorts and gas might shed some light on what's going on.
Lou Rossi Designs
Printed Circuit Design & Layout,
and Schematic Capture
Printed Circuit Design & Layout,
and Schematic Capture
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Re: Power tube failure modes
If that's a gassy tube then it may not take even a signal load being developed in the output stage for it to arc, but yet not burn open and truly physical short out sections of the tube.
Better for tubes, circuit parts and scokets to arc/ burn up then the big OT like that amp has to developed shorted windings!
Better for tubes, circuit parts and scokets to arc/ burn up then the big OT like that amp has to developed shorted windings!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Power tube failure modes
Lou, I have a Knight tube tester that tests shorts, emission, and gas. This tube passes all tests.
I build and repair tube amps. http://amps.monkeymatic.com
Re: Power tube failure modes
(1) has this happened once, or more than once?
(2) if more than once, is it always the same socket?
Remember:
One time is an accident.
Twice is a coincidence.
Three times is enemy action.
(2) if more than once, is it always the same socket?
Remember:
One time is an accident.
Twice is a coincidence.
Three times is enemy action.
Re: Power tube failure modes
Thanks, RG! This is the first time I've seen the amp. The tube sockets are ceramic, easy to access, and are free from carbon, though there was smoke residue on the ceramic from the burning resistors, which cleaned up with alcohol.
I build and repair tube amps. http://amps.monkeymatic.com