This circuit is from a 1965 Electronic Design. The transistors may be general purpose and the power supply must be symmetrical.
This circuit was found in a 90s Wels' Think Tank. The frequency depends on C2 and R3. The handset...
The circuit shown is from the 1994 Linear Applications Handbook by National Semiconductor. The...
This zero-crossing switch circuit triggers an SCR when the input voltage goes through zero. The...