Two types of Zr-coated dispenser cathode for cathode ray tubes (CRTs) have been developed and their practical application has been realized. The heater powers of these cathodes are 1.31 W and 0.76 W. Life tests up to 42,000 h were conducted at two levels of cathode temperature. Based on the emission residual ratio, stability of the Ir layer and the size of ion-bombardment nicks, it was found that the minimum life expectancy was more than 70,000 h, A heater for CRTs is used in conditions where a voltage of about 200 V is normally applied between the heater and the cathode. Therefore, it is important to design such a heater so as to lower the heater temperature and to develop a coating layer with high dielectric strength. In order to solve this problem, a new coating layer has been developed. A life test has been conducted for 39,000 h with a voltage of 300 V applied between the heater and the cathode, at several heater temperature levels. From the results obtained, the minimum life of the newly developed heater is estimated to be more than 80,000 h. (C) 1999 Elsevier Science B.V. All rights reserved.
