We found this circuit in the December 1968 issue of Radio Electronics magazine. The circuit is used with high-impedance magnetic headphones. The transistors are from that time.
This circuit was found in a 1965 Radio Shack documentation. The transistors are from that time....
This is a typical source of the time (1989) using the well-known regulator integrated circuit 723....
The integrated circuits used in this circuit are from the 70s and are therefore no longer common in...