Used in radio reception, this circuit was found in the February 1983 Radio Electronics magazine. The integrated circuit is the NE570 IC, and the power supply is 3.6 V.
Using an operational that is not common today, but which admits a modern equivalent, we found this...
This simple source of up to 1 A can supply voltages according to the secondary of the transformer, in this...
This interference rejection circuit for telegraphy was found in a 1980s documentation for radio...