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'noise and squeal'
Author:steve25 (registered user: 2847 posts )
Date: Mon, Mar 20th, 2017 @ 07:00 ( . )

Place a clip lead short across each preamp tube plate load resistor ( no plate load resistor = no gain ) but for the PI section, when the noise stops you've found the gain stage with the issue, or it's the next one back up stream towards the input jack.

At that point I would start confirming that any Cathode bypass caps have not shorted and in the same vein you do not have any failing power supply filters ( starting to short out) and yes new parts like electrolytic cans can go south from not being used!

Another way to go is to to set the amp volume wise so it just acts up, and then use a screw driver to to do a grid tap test as you progress back up to the input jack, the taps should make louder and louder crackles untill you get the failed gain stage.

Just two days ago I turned on one of my Bass amps that I had not used in over a year and it blew a fuse within 10 seconds of being on!
No that this relates to your issue, but always test your gear before heading out to a gig!!

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