Use of high-emissivity coating for picture-tube heaters

This paper discusses the advantages gained in television picture-tube performance by use of a new high-emissivity heater coating. Analysis of the heat-transfer rate between the normal alumina-coated electron-tube heater and the cathode indicates that a significant improvement can be expected if the emissivity of the heater coating is increased. Experimental confirmation of the anticipated improvement has led to the development of a dark, non-conductive heater coating. This coating, initially used for receiving tubes, has been found both beneficial and practical for picture-tube heaters. The advantages of the "dark heater" include improved "sag" characteristics, greater burnout resistance, improved heater-cathode arc-over resistance, and greatly improved reliability due to the lower wire temperature in operation. The important design considerations are discussed with respect to physical geometry and electrical characteristics.