This circuit was found in a 1967 General Electric documentation. Tunnel diodes can oscillate at very high frequencies. These are not currently easy to obtain components.
This circuit of an old publication produces the insect-like noise that drives them away. The...
This oscillator with FET was found in Popular Electronics from the 90s. This traditional...
This useful instrument has dual function, operating both as signal injector and continuity tester. The...