#1
I have this Marshall solid state 5210 112 combo amp from back in the early 80s. My girlfriend's dad gave it to me because he couldn't get it to work (the knobs needed a bit of a jiggle). I got it to work and it sounds incredible, but whether there's a guitar plugged in or not or if all the controls are at 0 but it's on it has this constant loud crackling/popping noise that's really annoying. I know it's not the outlet, electronics by it, ect. Can anybody help me? Thanks! It's sort of important because it's my gigging/band practice amp.
Gibson Les Paul Traditional Pro
Fender Blues Jr.
Dunlop Crybaby Wah
Ibanez Tubescreamer TS9

THE WHO
#2
could be loose/dead capacitor over the speaker.

may have worn out or the solder joins might have come off old cuircuitboards like that.

can't really help tho 'cept look for a big capacitor
Failure to prepare is preparing to fail
#3
I actually think it's the master volume knob somehow... When the channel volume is up the the master's off I can hear the guitar a bit but there's no crackling and even when there's no guitar there's no crackling then. I'll check what Hungry said though, thanks.
Gibson Les Paul Traditional Pro
Fender Blues Jr.
Dunlop Crybaby Wah
Ibanez Tubescreamer TS9

THE WHO