Also, Fair Radio Sales still has a bunch of bits and pieces for the PRC-8,-9 and -10. The AM-427/U cans are actually IF amplifiers and not capacitors. Sometimes they're sold by lot on Ebay - in fact, I think there's an auction running now. I haven't played with them for awhile now but I remember most of the problems being very low received signal level and/or very low rx audio. One radio I dove into had that problem and it turned out to be one or more of the AM-427/Us, from what I recall - one of which bore manufacturer markings in Vietnamese
The other
pain-in-the-@$$ was off-frequency transmit which you'll tear your hair out over if you're fiddling around with home-made battery packs BUT which largely went away in my case the minute I went with the inverter power supply instead.
I had a bunch of bad H-33/PT handsets and M-29 mics (the type with the U-77 connectors that these older family radios use) which made for very low modulation so people on the receiving end kept telling you that you were talking too softly. One old ex-VN radio guy took one of my handsets, rapped the mic-end on the corner of my jeep fender a couple of times, then told me to try it again. Voila! Worked perfectly. Turns out they're carbon element type and the carbon powder inside the mic element itself sticks together over time/ moisture exposure, and giving them a good rap *can* restore functionality -- elsewise they're doomed.
Fun sets to play with, but a good, stable, power supply is key before you start trying to troubleshoot or align them. And testing on-air between two questionable radios will be an exercise in chasing your tail. Been there. Got the medal.
