Found in an Electronic Design from the 90s, this circuit uses components from that time and can supply voltages of 5 V with current up to 100 mA.
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...