This 1-transistor circuit for currents up to 50 mA was found in the August 1974 Radio Electronics magazine. The transformer is 50 to 200 mA.
This control for motors with current up to 1.5 A was obtained in a 1989 publication, but it can...
This circuit is from an old documentation. However, it can be designed based on modern transistors...
We found this circuit in a 1976 documentation, but it can still be easily assembled using BC548...