Sure its not the heat ???,,, had exactly the same problem yesterday,,,line check only,,,all ok....occasional buzz in couple of songs,, then,,,,, silence...
Everything else plugged into the extension was fine,,,,,, ripped out the DI out the amp,,, went straight DI through the floor pedal,,, engineer turned up the bass in the monitor,,,,,,, survived the gig,,,,,,feck it was hot in there,,,, and the 5 hours in the van didnt help...its now working A1 again,,, which worries the hell out of me..........top of the head suggestion was thermal cut out ???,, never had problem with this amp before,,, and its done a lot of work.....dunno......fingers crossed really,,, cos if lose faith in a piece of road gear,,it will end up in the garage !!