This circuit is from a Popular Electronics from the 90s. It uses an opto-coupler with SCR directly controlling a 20 mA current load.
Suggested by the General Electric Hobby Manual of 1965 this circuit measures voltages from 0 to...
This circuit was found in an American publication from 1968. The transistors are from the time,...
The source shown in the figure provides output voltages in the range of 1.2 to 25 V with currents up...