Abstract: A settable resistor has a resistance path array (4) to which is allocated a contact piece (9) which is guidable in the longitudinal direction (13) over the resistance path array and has an adjusting device for the position of the contact piece. In order not to restrict the free displacement travel of the contact piece with a simple construction independent of the setting of the adjusting device, so that a high resolution is achieved particularly for application in the hand switch of a power tool with speed control regardless of a set maximum value, the contact piece (9) is additionally adjustable transverse to the longitudinal direction (13of the resistance path array (4) by means of the adjusting device (11).

Abstract: A circuit arrangement for regulating the rpm of an electric motor having series connected field and armature windings 1, 4 comprises a controllable rectifier 5 which is connected in series with the motor and is controlled by a phase control unit 30 as a function of a control signal obtained at armature winding 1 and conducted via an operational amplifier 12. To achieve a very constant rpm and a high regulating speed with simple means, each terminal of armature winding 1 is connected to one input 10, 11 of a differential amplifier 12 whose output 15 is connected to one input 19 of a comparator. At its second input, the comparator is given a desired value signal which is changed in dependence upon the current flowing through armature 1.