This circuit is from a 1968 documentation using one of the first integrated circuits available at the time, the TAA370. The circuit is powered by 1.3 V using a 200 ohm handset.
We found this circuit in an old American documentation. SCRs can be modern equivalent types. The...
When the voltage exceeds the value given by the zener, this circuit from a 1990 documentation...
This circuit was found in a 1970s documentation. The components are from that time, and...