Found in a 1960s RCA manual, this circuit uses components from the era. For the indicated circuit R1 is 28ohm and R2 is 1 k.
This circuit was found in Japanese documentation from the 1960s. It is a commercial circuit with...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...
This simple receiver for listening on the phone was obtained in a 1960 documentation. The circuit is...