Found in old American documentation, this circuit is intended for the control of heating elements. The SCR must have current according to the controlled load. Transistors are from the time.
Here is a simple source without a transformer for currents up to 50 mA. The voltage depends on the...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This circuit drive an LED with constant current determined by the values of the resistors of 10...