An ac bias operated multivibrator for dc to polyphase conversion is presented. The multivibrator introduced here is of multicore construction, having the number of saturable cores equal to the number of phases. It has several common windings wound through all the cores and two or more separate windings wound on each of the cores. A multivibrator is constructed with the common windings and two transistors. Of the separate windings, one, acting as a bias winding, is connected to one of the common windings to receive ac bias mmf, and the others are used as output windings. By keeping the proper distribution of mmf's among the bias windings, the proper sequence is kept among the induced emf's in the output windings, and hence the polyphase voltages are produced. The same principle can be applied to a polyphase multivibrator with a multiaperture core.