National LM378 amplifier is used as a basis for economical proportional motor speed controller. This integrated circuit is able to deliver 700 mA continuous current for such DC motor applications such as antenna rotors or motor controlled valves.  The basic of proportional control is as simple as amplifying the error signal to produce an action in such direction that minimize the error. This error  signal is generated by a mechanically coupled potentiometer wired in a Wheatstone bridge R1-R2-P1-P2 configuration.  The potentiometer P1 is coupled to the motor shaft  to sense the actual speed of the motor, act as continuous feedback sensor.

24 V DC Proportional Speed Control circuit schematic