A univoltage electrostatic lens for television cathode-ray tubes

The need to conserve stocks of scarce materials has prompted an investigation into the possibility of using an electrostatic focusing system for magnetically scanned television picture tubes. Such a lensfocusing system, requiring only a low voltage for focus, would be desirable; if the voltage is that of the cathode, the lens is termed a univoltage lens. The design considerations are discussed and a prototype gun is described. The characteristics of tubes using this type of gun are given and compared with those of standard magnetically focused tubes. The results at present available indicate that mass-production tubes operated with a final-anode potential below about 12 kV will require a low adjustable focusing-voltage supply. This is necessary for adequate resolution in all tubes. For final-anode voltages above 12 kV it is expected that good resolution can be maintained with the focus electrode connected to the cathode, notwithstanding the minor dimensional variations which will occur in bulk production.