ad30tc combo technical difficulty

[stdfan]

i have had a ad30tc combo amp for just over a year but hvae only recently played it loud for the past couple of weeks. the other day the first channel started to swell in and out and no the first channel humms while the second channel stil sounds outstanding. we took the amp out of the chasis and plugged it into a messa boogie cab it sounded fine then we took a jcm 200 and put it through the combo amps v30s and it sounded fine any pointers thanks josh