I found those MPSU transistors and bought some. Cool. But I think this board was too trashed by a couple previous techs who tried some very peculiar 'fixes'. Anyway, time to pull that channel's heat sink / circuit board assembly and use an external power supply so I can get at some test points and figure out where the internal damage is to this double sided circuit board.
Traces are literally falling off this thing and I believe there are shorts in the actual board material (like I have run into in some Adcom amp circuit boards). I have an ugly feeling I am going to have to fabricate a circuit board for this SA/4e. At least the S550 is a happy camper. Been enjoying that guy for a while now. Usually I find that I like a transistor amp for a little while then go running back to my own design EL34 tube amps. But this old Threshold is still pleasing to the ear.. really nice design. So I am really intent on getting this old S4/A running. I hear this old girl is supposed to be even warmer sounding (and warmer to the touch!). I have the one channel working. but the other is another story with that goofed up circuit board. These things run so hot as compared to the McIntosh amps. Those things run cold as ice, but still sound good. Still, I think the Threshold invokes a tad bit less ear fatigue then, say, a MC500 or MC352. But, I certainly could live with any of them. Just wish I had the kind of money to buy an example of each.. Oh well, maybe I'll win the lottery.. Yea, right.
Traces are literally falling off this thing and I believe there are shorts in the actual board material (like I have run into in some Adcom amp circuit boards). I have an ugly feeling I am going to have to fabricate a circuit board for this SA/4e. At least the S550 is a happy camper. Been enjoying that guy for a while now. Usually I find that I like a transistor amp for a little while then go running back to my own design EL34 tube amps. But this old Threshold is still pleasing to the ear.. really nice design. So I am really intent on getting this old S4/A running. I hear this old girl is supposed to be even warmer sounding (and warmer to the touch!). I have the one channel working. but the other is another story with that goofed up circuit board. These things run so hot as compared to the McIntosh amps. Those things run cold as ice, but still sound good. Still, I think the Threshold invokes a tad bit less ear fatigue then, say, a MC500 or MC352. But, I certainly could live with any of them. Just wish I had the kind of money to buy an example of each.. Oh well, maybe I'll win the lottery.. Yea, right.