Found in na 1969 Electronics World, this circuit makes use of transistors of the time. Equivalent transistors can be used. The diodes can be 1N4004.
This circuit simulates an inductor. Or operational amplifier of old type, but a configuration is...
We found this circuit in a 1967 Electronic Design. The circuit uses contemporary transistors that...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...