This Intersil circuit was found in a 1980s documentation. Operational are of the time, but current equivalents can be experienced. The graph with the circuit performance is given next to the diagram.
We found this Vox in a 1969 Motorola documentation. Transistors support modern equivalents and the SCR can...
Suggested by Texas Instruments in 1968 documentation, this circuit uses components from the era....
This very low frequency circuit was found in a 1964 Electronic Design. Transistors may be modern...