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FDP Forum / Amp Mods, Repairs, and Projects / Shorting guitar pickup fries preamp tube?

jazzguy

Philly, B-3 Capital

don't dream it be it
May 22nd, 2017 02:11 PM   Edit   Profile   Print Topic   Search Topic

couple weeks ago someone sat in on one of my gigs and plugged his guitar into my '67 Twin.
There was a very loud hum the whole set, I guess a grounding issue?
but the next day the amp would make a loud crackling/distorted sound whenever I played a little louder, I checked the tubes and found a bad 7025 in V2.
replaced w/a nos RCA and the amp really came alive, I guess the old tube was on it's way out for awhile.
the guy sat in again yesterday, same loud hum and after 2 tunes the amp exhibited the same crackling/distorted sound.
haven't had a chance to check the tubes again, but it it possible a shorting pickup or cord could blow the preamp tube?

DrKev
Contributing Member
*****

Paris, France

It's just a guitar, not rocket science.
May 22nd, 2017 03:05 PM   Edit   Profile   Print Topic   Search Topic

"but it it possible a shorting pickup or cord could blow the preamp tube? "

No.

Crackling/distorted when playing louder suggests something moving. Clean and retension the tube sockets? Also look for broken solder joints her the tubes. As the insides of the amp heat up, things expand and connections break and crackle.

jazzguy

Philly, B-3 Capital

don't dream it be it
May 22nd, 2017 03:25 PM   Edit   Profile   Print Topic   Search Topic

thanks Kev, I didn't think so.


amphead4

Cincinnati, USA

May 23rd, 2017 12:01 PM   Edit   Profile   Print Topic   Search Topic

If his guitar had an active circuit that suddenly hit the input jack of your amp with battery DC, you would hear a big pop as the bias of the first stage shifted. But even then, the plate load resistor should limit the current so that the tube couldn't run away and burn up.

I'm thinking tube socket with dirty or loose contacts. Could be the old tube is still good too.

FDP Forum / Amp Mods, Repairs, and Projects / Shorting guitar pickup fries preamp tube?




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