This circuit was found in General Electric documentation from 1968. The circuit uses triac from the time as well as transistors that can be replaced by modern equivalents.
This audio oscillator circuit was found in a 1992 publication. In the original article it is...
The integrated circuit used is a dual 555 CMOS. The circuit is from an English documentation and...
This 3V-only circuit was found in old American documentation, but can be implemented with...