Cathode-Ray Picture Tube with Low-Focusing Voltage

Wide-angle picture tubes, high anode voltages (reduced magnification and beam divergence), and the need for material conservation prompt replacement of magnetic with electrostatic focusing. There are considerable advantages in a unipotential lens focusing system designed to obtain optimum focus with the focusing electrode operating at 0 to 5 per cent of the anode voltage instead of at the customary 20 per cent. The focusing electrode may then be connected to the cathode or to a potentiometer across the low voltage dc supply of the television set. A successful tube design is discussed and operating characteristics given. The voltage breakdown problem, which is stringent owing to the high-voltage gradients at prevalent high anode voltages, is considered.