cory, cool set! It looks very much like a ctc25. That big heatsink for the A-output gives it away. Check that purple colored stamp on the back of the chassis. JS is right on those discs. Called thermistors, they conduct when they are cool and stop conducting when they get hot, which is why the leads start to come off. You will noticed the pcb diccolored around it too. If the leads break off, which is so very common, or atleast looking like they are starting to separate, you can just solder them back on and they are good as new.
Anyways,
Let me know your model number, I can check my parts manuals. I think I might have some knobs lying around. If not, moyer has lots of good stuff for those sets still
I just bought some from them not too long ago for my ctc38.