Mark III Problem

[Countryguitar99]

I'm having a problem with my mark III black stripe no eq no reverb combo. I usually run a clean boost in the effects loop for a solo boost and it's always worked great. The last gig it only added distortion no volume boost. I also noticed it seemed my lead volume fluctuated a bit. I tested my pedal through my backup amp, peavey classix 30, and it worked fine.

Could his be preamp tubes causing the issue? My band is fairly good quiet usually only on 3 on the master so it shouldn't be a headroom issue. Power Tubes are relatively new not sure on preamp. Thanks in advance!

 

[tony777]

Two things to check, though I'm not a tech.
Does the volume drop when you don't have anything in the loop?
If not, try to clean the FX loop jacks.
If you have a spare preamp tube, try to replace one at a time to see if the problem goes away.