Thanks to everyone who replied to my post. Here's the story on my newly acquired 4100:
I picket up the receiver from a friend who had it sitting in his closet (along with a lot of other super-cool McIntosh equipment). We fired it up and it worked fine for about 2 minutes. After a few minutes of operation, the left channel power indicator pegged into the red and the speaker protection relay contacts started to glow (literally). We quickly turned the receiver off and after a few minutes we tried again with the same results. We took a closer look at the speaker protection relay (Eagle 48v) and the contacts were fried. We cleaned it up as well as we could and tried again with no change (still cut out after a couple minutes). My friend concluded that replacing the output transistors would resolve the problem (I was skeptical). In any event, I replaced the original output transistors (RCA 132188-9) with ON MJ15003-4 and now the speaker protection relay does not operate (no voltage at the coil) and I get no response from any of the 3 speaker outputs on the 4100. The preamp and associated inputs (AM, FM, Phone, etc) work fine when I route the preamp output to an external amp. I'm guessing the problem is either in the channel drivers (045219) or maybe the power supply board (045217). I am hoping someone might be able to help me identify some tests I could perform to isolate the problem. My intention is to eventually restore the 4100 but my first step is to get it working. Any assistance or advice would be greatly appreciated! Thanks.