For experiments with a disk rotating at various speeds, the April 1998 Electronics Now magazine suggests this PWM motor control. The current with the LM317 is 1.5A maximum.
This preamp version uses BC109 transistors that are older versions of the current BC549 in plastic...
This circuit was found in a 1980s documentation, using a comparator from the time. The...
I found This circuit is in a documentation of transistors from 1958. It uses germanium PNP...