Some Reliability Characteristics of CRT Cathode Assemblies

Six types of CRT cathode assembly are described, including the traditional cap-cylindrical shank-ceramic wafer assemblies which have been in use for many years and two of the more modern heat-shield assemblies. The range of operating temperature is no larger than 60 K for either of the heat-shield assemblies and may be as large as 295 K for the older types. Spontaneous variations in temperature of up to 97 K, downward drifts in temperature of as much as 40 K after peak temperature has been reached, and increases of up to 154 K as a result of reprocessing have been observed. These effects are generally much smaller with the heat-shield assemblies. The 60 K range of the heat-shield assemblies implies a variability of more than 4 to 1 in life and performance. The ranges of the older assemblies imply a variability of from 64 to 1 to more than 1000 to 1. The spontaneous variations in temperature are responsible for appreciable changes in the grid bias required to obtain a fixed value of beam current, or, conversely, large changes in the beam current obtained at a fixed grid bias.