This circuit was found in a 80s American documentation. The zener diodes determine the points of action of each stage and the transistors can be general purpose types.
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...