This circuit from General Electric was found in a 1967 documentation. The SCR is of the time, as are the transistors, but equivalents can be used.
The sensor in this circuit is a common transistor like the BC548. The circuit is from a 1979...
With this circuit it is possible to control a relay up to 100 mA with an extremely low input...
Found in an Electronic Design of 1964, this circuit is intended to the signal amplification in the 88 to 108...