OXIDE CATHODE AND PRIMARY GRID EMISSION STUDIES.
Monthly rept. no. 11 for Mar 48,
WESTINGHOUSE ELECTRIC CORP BLOOMFIELD NJ LAMP DIV
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Efforts have been continued to determine the cause of arcs in the 715 type tube by photographing oscilloscope traces of control grid current vs cathode current. A change of cathode ray tube to a 5LP5 having a blue screen and an intensifier anode has resulted in some improvement in the trace photographs. Single transients such as occur at the time of an arc, however, have not been successfully photographed. Difficulties due to breakdown of components in the test equipment have been overcome. The thermionic emission of zirconium-clad molybdenum has been investigated both when the surface is clean and after it has been contaminated by the material evaporated from an oxide cathode. The probable values of thermionic constants for the clean material are Phi 4.11 e.V. and A290 ampcm2deg2. Values of Phi and log A from measurements taken at various stages of heat treatment show a linear relationship. The values for the fully contaminated condition are Phi 2.26 e.V. and A40 ampcm2deg2. The contaminant is not stable on zirconium at temperatures above 800 K. Zirconium is not as good a grid material for use with oxide cathodes as Svea metal or carbonized niclel. A supplementary report has been written on grid emission problems in a commercial tetrode with an oxide coated cathode. Author