Hi, from RR. It is indeed American, it's a Rowe-AMI R74 from about 1976. I'm only working on the audio side, I'm not touching the mechanism, no chance, I'll leave that to the experts, that bit works thank goodness. I've just got a spare s/h preamp from a place in Middlesex, I think you're right about the in house numbers as all the transistors have got very similar numbers and packages, a bit like TO92's but not quite the same. One has shorted and fried a resistor which still has it's colour code intact, and another transistor has a cracked package. My mate has the manual with the circuits so hopefully the right numbers will be in there. The whole preamp runs on 24 volt so there shouldn't be any problem with voltage ratings but I know some of the circuitry is a bit odd, with features like AVC and a discrete DC volume control, and a fancy feature that boosts the bass at low volume levels. It's all transistor, no chips, but lots of diodes, and it's all silicon apart from one diode. RR.