the convergence circuit has the bridge type rectifying circuit and the first potentiometer parallel - connected to this rectifying circuit and having the slide which is connected to the output terminal at the hot side of the rectifying circuit and moved to alternatively vary the waveform of the correction current of the output of the rectifying circuit every half cycle . on the other hand , the second potentiometer and the series circuit consisting of the resisting means and the correction coils are parallel - connected to the output terminals of the rectifying circuit , and the slide of this potentiometer is connected between the resisting means and the correction coils . the value of current flowing in the correction coil is adjusted by moving the slide and the adjustment of the second potentiometer is optimized by selecting the resistance value of the resisting means .