The presented circuit uses an optocoupler to trigger a triac. We found it in a Popular Electronics from 1992.
We found this simple transistor tester in a French publication in 1981. It uses a common analog...
This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit is...
We found this circuit in Ferranti's 1974 transistor manual. The components are from the period. Note...