These are an interesting amplifier. They can be run in class AB or class A; at the press of a button on the front panel the bias changes making the amplifier run hotter and hopefully sound better at the expense of some output power. I ended up with two of these amps, both faulty in similar ways. One had no sound at all, the amp powered on, the input selector light moved but no input was being selected, the front rotary switch operates relays on the input board, there was no sound of the relays operating. The other amp had powered up and played music but the signal would come and go and sometimes be distorted, it was random, rotating the input selector switch sometimes made the signal return, changing the inputs, made little difference. After making some measurements I decided the power section, on its own board, was working (on both amplifiers) the problem seemed to be, on the first amp, no power to the input changing relays. The tone board, attached to the front panel, has a power supply that runs the tone amp, the front panel lights and input switching board including the relays; this board was dead the fuses had blown. The fuses are not glass cartridge fuses but small plastic cased fuses soldered onto the circuit board, I had to remove the front panel to get to them and measure them to find they were blown. Fuses like this rarely blow for no reason, I suspected a relay coil had shorted, unusual but not unheard of; I removed the input board and measured all the relay coils (while still installed) all seemed OK except for one, sure enough a dead short, I removed the relay and checked again BUT it was OK, the short was the associated 10uf 50 volt capacitor, the capacitor was a dead short, now that's a little unusual, electrolytics often change value but don't go dead short that often. I replaced said capacitor (I happend to have identical Nichicon, same series as was in there) and put that input board in the other amplifier that had strange fading and distortion, bingo that amp now goes well!! So the other input board has some problems albeit slightly different, I made some measurements and sure enough it looks a little dodgy.....updates later this is a work in progress. Update: being an older amp, the relays have been operating for many hours and I think the contacts are compromised/dirty, the circuit board looks like it has been hot, so the relay coils are running hot for long periods and the relay contacts get a film of "dirt" that stops them conducting well - solution, replace the relays! all 13 of them... with Omron G5v-24 (the original NEC MR62-24us ones are no longer available, no NEC equivalent is made), I chose the high sensitivity version Omron, H1 designation, not much more expensive but able to handle higher over voltage and hopefully not get as hot, so they should last much longer than the originals I'll post more photos later also... So one amplifier working the other diagnosed. The working one is being soak tested after adjusting the bias for both class AB & class A operation. How does it sound? Wow what a nice sounding amp...I set this up with B&W DM4 speakers and a mid-level Sony CD player, I was very pleasantly surprised, great sound stage, detailed mid-range and really nice controlled bass and much more bass than I was used to getting from the DM4's, class A after 15 odd minutes of warming up only improved the sound ... a little but enough. I'd be happy with this amp as my main amp. The DM4's were handy for testing but it may be a luck pairing, they rarely sound so good with lesser amps as they are so revealing, they show up flaws in anything but the best.