hi i'm a first timer working on my peavey mark III. i've used the amp (for guitar, though it is a bass amp) consistently for 3 years without a problem. last week at practice i hit a chord and loud, awful hum came out. the heat sink was red hot. the hum persisted with or without a guitar plugged in until i shut the amp off. today i tried it again and the amp functioned for about a half hour and then the same hum. i opened her up and found one burned looking resistor. if i'm reading right it's 4.7 ohms. could this be all or part of the problem? thanks.