This circuit indicates when the voltage of a 12 V battery is low. With changes, for example, the zener, the circuit can be used to monitor other voltages.
This 1-transistor circuit appeared in a February 1962 Radio Electronics. The coils for the...
This recyclable automatic timer was found in Radio Electronics magazine from July 1960. The...
This transistor tester was found in a publication by Gernsback from 1960. The circuit can be used...