This transistorized circuit appeared in a Radio Electronics magazine in March 1958. The frequency range depends on the tuned circuit, being within a few megahertz.
This voltage inverter circuit is from a Radio Eklectronics from October 1965. It was used in...
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
The circuit presented was found in a 1988 documentation. It consists of an alarm siren that it...