i use an ampeg b2r head with an ampeg 8x10 cab. whenever i gig my amp will just short out on the last song or so. it will still stay on, but no sound will come through. i have to turn it off and back on again for it to work. but then it will short out again. it never happens in practice, only at gigs. could it be the clubs electrics or is it overheating or what? thanks.