Abstract: A chopper for adjustably controlling the average value of the voltage supplied from a D.C. battery source to a motor load for adjustable speed control. The chopper comprises manually-operable spring-biasing means for applying force to close a contact to energize the motor and electromagnetic means simultaneously energized for re-opening the contact. This occurs at a high repetition rate so that the average value of the voltage across the motor determines the motor speed. This average value of voltage is proportional to the closed-to-open time ratio of the contact and is adjustable by manual control. Two versions are disclosed. In the first version, the spring-biasing force is applied to the contact by depressing a trigger. In the second version, the spring-biasing force is applied to the contact by rotation of a knob. Both versions may use either tension or compression spring force.