Abstract: This alternator includes a stator comprising an armature winding and a rotor comprising a permanent magnet field. A sleeve is located between the rotor and stator and comprises on its periphery alternating ferromagnetic and nonmagnetic segments. When the ferromagnetic segments are aligned with the poles of the stator, the flux linkage between the rotor and stator is maximum. When the nonmagnetic segments are aligned with the stator poles, the flux linkage is a minimum. The sleeve is shiftable through 90 electrical degrees by means of a motor. The output of the alternator may be regulated between maximum and minimum values by so shifting the sleeve.