This circuit is from an American manual from 1975. The transistors are types of the time, but equivalents can be used, as well as the relay that can be according to the supply voltage.
In the figure we have the way to activate a red LED that needs 1.7 V or even others with higher...
This circuit was obtained in a 1979 publication, but it can be assembled with the BD135 instead of the...
Found in Radio Electronics from the 90's, this circuit employs a 3140 operational amplifier, still...