This small tone generator was found in the November 1987 issue of Radio Electronics magazine. The phototransistor is common and controls the sounds generated. The basic frequency is given by C1.
Two transistors on a regenerative switch are used to trigger a triac. This circuit is from the RCA...
This circuit uses a 555 (according to the diagram) to generate 50 ms tone bursts at a frequency of 1.5...
The radio presented was found in a 1980 documentation. It consists of 3 stages: the tuning circuit...