2001 Fender Twin Amp Losing Power and Distorting

[yesguitarman]

My 2001 Fender Twin Amp has recently started to lose volume and distort 3-5 minutes after powering up. Prior to the drop in volume it sounds fine for the first few minutes. This sequence is repeatable. I replaced the #1 tube (the 12AX7 pre-amp tube) to no avail. Any thoughts? Other than replacing the pre-amp tube and previously, the 12AT7 reverb tube, no other work has been done to the amp. The power tube condition indicator LEDs on the back remain green.

Any thoughts?

Thanks!

[Enzo]

probably not a tube anyway, what made you decide to change that one tube?

Patch across the FX loop jacks, any help? Patch across the pre-out and powr amp in jacks, any help?

Use those jacks. When it warms up and fails, plug the guitar or signal source into the powr amp in jack, is it still low and distorted or clean? Now plug into the FX return instead, is it now low and distorted or clean? These tests isolate the issue to the power amp or the later half of the preamp. Likewise play into the regular input, and run a cord from teh FX send to some other amp. What comes out the othe amp? Low and distorted or clean and strong? And again, run a cord from the preamp out jack to some other amp. Same questions.

[Raybob]

2001, probably electrolytics. They didn't use the best brands in those, and it is 16 yrs old. Much of my biz is rebuilding RI Fenders into hand wired.