the saturable reactor employs two dual drum cores having two winding portions which are sandwiched by two common permanent magnets to statically bias the magnetism . each winding portion of each drum core is wound with two impedance coils which are individually series - connected to the either of two horizontal deflection coils . two drum cores are inserted into the common control coils . when a horizontal deflection current is supplied to the impedance coils and a vertical deflection current is supplied to the control coil , the current which flows in a pair of horizontal deflection coils varies differentially in a vertical deflection cycle to minimize misconvergence .