Damaged in shipping. The A channel would cut in and out and also the B channel was very noisy. Very hard to find the intermittent, which turned out to be the treble pot on the A channel IIRC. Replacing a few transistors in the B channel preamp seemingly eliminated noise but unfortunately it was not banished completely. Certain very particular control setting combinations would still bring noise on the B channel and the source was never found.
470 circuitry is braced between metal brackets on front, back and sides, so the whole top and bottom of the PCB panels is accessible. Makes it kind of easy to work on, until you have to access the component side of the preamp boards. Then it’s time for major disassembly.
Anyway, word of warning to 470 owners — the huge power supply cap mounted to the back panel chassis is centimeters away from the reverb tank, which is at ground potential. Acoustic placed a piece of foam on the reverb tank here so the cap doesn’t short to ground, but that was like 40 years ago and the foam is probably dust, like it was in this 470. If the amp gets really shaken up or the cap becomes loose in the bracket it will eventually make contact and short. Sparks will fly. Bad stuff may happen. Put some electrical tape or something on the reverb tank to isolate it just in case. Also make sure you drain the cap of any remaining voltage before doing this so you don’t potentially get shocked.
Amazingly putting out 166W into 4 ohms. This mystified me at first as it was about 10 more watts than my 370 put out at the same impedance. The key is the 370 can go to 2 ohms and yield more power still. The 470 cannot. No more need to wonder ?why?
Complete Acoustic 470 service manual and owners manual. It literally tells you everything.
As an aside there are two different versions of the power supply/output section PCB. I backlit them one day when I had multiple 470s. The PCB layout is completely different. PCB on left is 170051-A. Right side is 170045-?. Disregard the middle PCB it is the preamp of one of the amps.
And from the component side.