Thermionic vacuum tubes

The paper commences with thermionic theory, and, after quoting Richardson's well-known equation, states that the filament efficiency or thermionic emission i for a given filament power w is generally of main importance. Curves are given by C.J. Davisson showing the coordinates, the scales of which are not linear, as i and w and provided certain factors hold good the curves are straight lines. Different slopes are produced by plain tungsten, thoriated and coated filaments. An account of Wehnelt's lime-coated kathode leads to present development of coated filaments, and as an example the figure of 200 milliasmperes per watt with a life of from 25,000 to 50,000 hours is given. The process of producing coated filaments is described, including works manipulation, pumping and gettering. A table ia given showing the various types of valves made, together with data on filament and anode volts and amperes, and is followed by a brief description of some of the types and their applications to different circuits. Water-cooled valves up to 20 kW are described, the largest having pyrex glass and suitable for use at 17,000 volts. Illustrations of a number of valves are included, both small receiving valves, repeater valves, small glass transmitters and water-cooled valves.