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Is there a zener diode to regulate the power? Of course the 150V or so out of the rectifier was way too much for the circuit.
If it's 1970, it's probably silicon transistors and the power is positive voltage. That 10W green resistor is the main dropping resistor for the power. The heat sink for the output stage hides the transistors. But looking at the different styles of IF transformer, it really is a hodge podge of whatever parts they could find.
I have always felt sorry for those gullible fellas who paid good money for those correspondence courses. NRI is very old, National Radio Institute, and they go back before WW II if I remember correctly. (I go back before WW II also!) Wasn't that JE Smith the guy whose pic was in most of the early ads? Then there was Coyne, ICS, and CIRE (Cleveland Institute of Radio and Electronics).
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