This oscillator that generates signals below the audible range (sub audio or infrasound) was found in a 1965 documentation. Transistors are for general use.
This circuit using components that are still common in our market was found in a 1987...
The varactor or varicap diode tunes the signal for listening to SSB signals on a common receiver. The...
This circuit that also serves to control LEDs and other loads is from a 1960 publication. The...