This circuit was found in a 1964 Electronic Design. The components are of the time, and modern equivalents can be used. Note the multi-emitter transistor.
This 80's documentation circuit includes an amplifier of the era. Used integrated circuits are...
Based on an LM36000 OTA this circuit was found in the July 1988 issue of Radio Electronics...
This 1kHz filter with Q = 10 can be applied to any operator. The power supply is symmetrical and...