This circuit was found in an English publication from 1967. The circuit is for listening on a phone. Transistors are types of germanium of the time.
This traditional circuit was obtained in a 1974 documentation, but can be mounted today with the...
PIC16F19197 Microcontroller Family Combines Battery-Friendly LCD Drive with Core Independent...
September 2017 - Can be purchased from Mouser Electronics Triacs with 20 A and 30 A currents...