This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is not an easy component to obtain and the power can be supplied with a single button cell.
The purpose of this circuit is to measure the intensity of audio signals. We found it in the...
The battery charger suggested in the figure has its current limited by resistor R1. This component can...
This differential amplifier, found in a 1964 Electronic Design, has a gain of 30. The setting can be...