#1
 I have the Peavey Supreme XL SS head and I quite like it. Especially with a Boss DS-1 through the clean channel I've gotten exceptionally great metal tones. I acquired the head second hand from a buddy who didn't have a cab for it. I'm running into a Marshall 4x12 cab. Since the first plug-in I noticed crackling and cutting in and out when adjusting certain knobs. I also had issues with crackling when moving my lead around on either end while running straight into the amp from multiple guitars.
I cleaned out all the jacks, even ones I wasn't using and the lead issues have resolved. On my dist channel I no longer have the knobs issues either, but it is significantly quieter than my clean channel, which is having pot issues for the treble and mid(this one is the worst). I want to get the amp open to apply contact cleaner to all of them but I can't seem to figure out how to get to them. No matter what I take apart (carefully) I can't get to the inner workings of amp. When I adjust the mid especially my tone becomes vaguely empty and I lose a lot of sustain and fullness to it. It's subtle, because I don't lose any volume. It also overlays this terrible fuzz, that isn't particularly loud, but throws the tone off completely, even on a clean blues tone (Generally when playing in lower keys).

So my question after all that is, does anyone know how to get access to the pots? Also could this be the 250 fuse inside? And would dirty pots cause a loss of tone and add fuzz to EQ?

Thanks in advance 
#3
Due to its age you could have several things going on,  You need to remember this beast was built back in the mid/late 90's, And while still built in the US a lot of its components were made in China,  and not to be cheap, its just that's what was available at the time,   What worries me is the fact you cant figure out how to get it apart to even clean the pots,  let alone spot a bad cap or check values on various other components.  But don't get me wrong, that's a really cool amp, Old James Brown design and shares a lot with the Bandits, XXX and a few other Peavey designs,  Problem is, not many work on that stuff anymore, Its a dying trade, Sad as it is we live in a throw away world when it comes to electronic goods today,  So in this case even if you do figure out how to get it apart and spray some cleaner at it what do you do if the problem persists?  Well in todays world you'd send it off to the E Waste pile and buy a new amp,  If you really love it you seek out someone that can repair it,  In which case it could cost as much as it sold for new.   The rock and hard place so to say. 
#4
nastytroll isn't really wrong.  However, I would assume, like most Peavey amps, you will have to take off the feet to get it started.  

It is getting really hard to find people to fix amps now a days, and paying someone to fix a SS amp can cost almost as much, if not more, than it's worth.  But you never know.  I just paid $60 to have a pot and output jack replaced in my XXX (I had and supplied the parts I had ordered from Peavey).  Not too bad at all.
#5
Xander_X Yeah, a few hours after posting I did just that. And as luck would have it cleaning all the contacts made a great difference. The head seems to be in great shape. Everything inside is clean as a whistle now and everything else looks brand new. She sounds great. The XL has a slight fuzz in the Lead channel but this seems to be intentional. I like more of a barking, shhugg-ing kind of distortion and the DS-1 in front of the clean channel really does it. I'm getting an old Crate head on Tuesday as a secondary head/tone sculpting tool. The next step for me pedal wise I think is going to be an EQ. But overall cleaning it out and swapping the fuse for the hell of it seems to have done the trick. 

PS: Just incase someone goes looking in the future for how to get the chassis out, it's the bolts in the feet holding it on. I feel like an idiot for even having asked. 

Thanks to both of you guys for replies