This continuity test was found in a 90s Electronic Engineering. Transistors are types of general use of the time with equivalents such as BC548 and BC558.
This FM detector circuit was found in a 1977 documentation. The circuit uses a 1977 Signetics...
This very simple circuit turns on an LED when an object interrupts the light that falls on the...
This 1970 Philips circuit uses a mechanical counter. The circuit is triggered by a reed switch...