This circuit generates frequencies determined by R3 and C1. We found it in the Radio Electronics magazine of May 1988. The power supply must be symmetrical.
In the figure we have a typical detector stage for a radio receiver. The circuit is from 1963,...
Found in a 1968 Texas Instruments documentation this circuit uses an SCR from that time. Modern...
This circuit was obtained from an American publication of the 80's. The integrated circuit is of the...