Grid Temperature as a Limiting Factor in Vacuum Tube Operation

A method for determining the grid dissipation at which primary or thermionic emission from the grid begins has been devised. By means of suitable rectifiers and an alternating-current source, the grid is heated during positive half cycles and the presence of primary emission is determined during negative half cycles. A variation of this method also enables one to measure the grid dissipation limited by primary emissions when the plate is heated. Sample values of grid limits for individual tubes of familiar types are given. The effect of gas on permissible grid dissipation is briefly discussed.