This commercial circuit is from a Japanese magazine from 1967. It uses germanium transistors, and the coil can be made with 80 to 100 turns of fine enameled wire on a ferrite rod.
This simple oscillator is yet another of the many versions of sonic insect repellent that we find...
The circuit in the figure operates at frequencies from 4 to 20 MHz and also uses a common junction FET...
This TTL counter was found in the April 1979 issue of Radio Electronics magazine. The circuit is...