Found elsewhere in this section, but from other sources, this circuit is from a 1964 Electronic Design. The transistor is from the era and the power voltage depends on this component.
Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the...
This circuit with SCR and Unijunction and which can be assembled today with modern equivalents was found in a...
This circuit was developed to find intermittent defects in an electrical control. In the event of a...