JCM2000 TSL Losing low End

[dtd6string]

Hello,
I have searched this forum and cant find anyone with a similar problem. I have a JCM2000 TSL100 Head that after about 2hrs of playing losses all its low end.
The head has Groove Tubes in it and has been biased.

Please help.

[Mars Amp Repair]

HMMM,
Yeah, that's a weird one. Do all levels generally diminish along with possibly the bass dropping more?

I'm not certain how the loop jacks work on that amp, but you might be losing signal in the send jack switches. To bypass them, just run a 1/4" guitar cable from the 'send' to the 'return' jack. If your problem is solved, you can try to spray some contact lube/cleaner in & run the 1/4" plug in & out a few times to clear it up.

If that doesn't help you might take an output from the 'Send' jack of the loop on the back & feed it to another amp to try and isolate the problem to the preamp or the power stage. If the bass still dimishes from the send jack, then you at least know it's not in the power stage.

keep us posted. glen

[dtd6string]

I am running a pedal board through the loop. I will try what you have suggested. I keep thinking its a heat problem due to the time.
It only looses bottom end and goes to piercing highs. The volume levels on all three channels remain good.
Wouldn't a jack problem be there all the time?
I'll try this and post results.

[Enzo]

My first thought is losing the signal path and the remaining crosstalk will tend to be shrill. The cord from send to return is also my first suggestion.

Jack problems can be as intermittant as any other problem.