This circuit is from a March 1978 Radio Electronics magazine article that showed how to build it. The circuit is TTL based and is powered. The components used can still be found.
This circuit converts BCD inputs to analog voltages. The operational amplifier must be powered...
This circuit is suitable for the calibration of old analog oscilloscopes. It was found in...
This is the circuit of a hearing aid amplifier manufactured by Sony in the 1960s. The circuit was...