I bought a pair of these at the Goodwill for $1.50. It was marked $3 but I told the girl it wasn't worth it and she agreed. It's one of the strangest circuit designs I've ever seen, the volume control was originally attached to the output transistor as the emitter resistor! It took me a few days just to figure out what was going on, then I found that someone had screwed up the wiring at the factory so one of the units was a lot quieter than the other, due to some crossed wires. I re-designed the circuit so I could use it for a practice amp, but I left the "push-to-talk" button so that when you press it, the machine feeds back internally. It goes really well with my battery powered noise generator, but unfortunately that unit isn't very photogenic so you have to wait to see it until I get a better camera.
