a defective damper (i.e. 6W4), high voltage rectifier (i.e. 1B3) or high voltage regulator (i.e. 6BK4) tube. Early color television receivers also used a complex dynamic convergence system, which was driven by both the horizontal and vertical output stages. Failure of part of this system could overload either tube, though this author has never seen such a failure in person. Audio output tubes in radios, stereos, public address systems and guitar amplifiers (50C5, 6L6, etc.), usually due to a bad coupling capacitor upsetting the bias or a shorted load. If any tube presents a glowing plate, the equipment should be shut down immediately to avoid further damage. Vacuum tubes Electrodes