Four-Element Tube Characteristics as Affecting Efficiency

The variation in the ratio of grid and plate current of three-electrode vacuum tubes aroused considerable curiosity and the tests reported in this paper were undertaken in an endeavor to ascertain the laws of current division. It was found that in a tube having symmetrical electrodes, that is, straight wire filament, concentric cylindrical anode and cylindrical grid, made up of wires parallel to the axis, the ratio of grid and plate current was a function of the tube geometry and quite different from that usually found in commercial design. The ratio of grid to plate current in such a tube exceeds the ratio of projected grid area by only a small amount, easily accounted for by variations in the electric field around the grid wires. The considerable departures from this ratio in commercial tubes appear to be due to a combination of secondary emission from the tube anode and unsymmetrical arrangements of grid wires and supports.