In the shunt motor armature control circuit of Fig. 7.59(a) the Thevenin equivalent as seen by motor armature is drawn. The no-load armature speed is governed by VTH, which can be independently adjusted by the ratio R2 /R1. The series resistance
Similar arrangements apply for series motor potential divider control circuit of Fig. 7.58(b). In this case the motor no-load speed can be adjusted to finite reasonable value and so the scheme can be employed for production of low speeds at light loads.