The 136 is a  Superior POWERSTAT® Series 20A 120V single-phase Variable Transformer with knob rotation and epoxy-coated POWERKOTE® coils for long life. This transformer provide continuously adjustable output voltage from utility line voltage and features movable brush-taps ride on commutators, rotation of brush by manual or motor-driven means delivers any voltage in the range between 0 and 140v, greater ratings/overload capacities and better resistance to fungus, salt spray and other contaminants.