this amp is such a good buy.i have one from a similar year. i had my amp looked at by a local amp dealer who knows his shit, and he noticed alot of the circuitry used was parts that arent available or used now, and they are quite highly sought after parts. it was on the pcb..i could get details if anyone wants to know, but he said that mesa and most amp makers in general dont use those parts anymore. he mentioned they sounded heaps better than current materials used. this would make this amp a way better mark IV buy than anything else available. someone is gonna get real lucky with this one.