This is the 1968 MR480 commercial cassette recorder circuit. The circuit was fully transistorized and powered by 4 large batteries. We found the diagram in a Japanese documentation of the time.
This configuration makes use of currently uncommon components. In fact, we found it in...
This 1 kHz oscillator was found in the February 1970 issue of Radio Electronics magazine. It uses...
This circuit was found in Motorola documentation from 1968. Transistors can be modern equivalents, just...