A transformer having variable reluctance, that controls the amount of power conveyed from an input to a load, based on a value selected by a computer control. The load power is varied by controlling the section and air gap between two parallel iron cores and a magnetic reluctance shifter positioned between the cores to vary the magnetic reluctance. The shifter is rotated by a motor. The position of the shifter varies the reluctance of the transformer and thus varies the amount of voltage transmitted from the primary winding to the secondary winding of the transformer. The iron core transformer is mounted in a non-magnetic frame and the windings are made from insulated braided copper strips, or insulated twisted cable.