The Developmemt of Electron Tubes for a New Coaxial Tramsmission System

AS THE demand for long distance telephone circuits has increased, new transmission systems capable of handling more channels per conductor have been developed. Also the advent of television has created a demand for broad band channels for network facilities. One of the latest developments now nearing completion is the L3 Coaxial System. Three new tubes have been developed specifically to meet the exacting requirements of this system: two tetrodes, the YV.E. 435A and W.E. 436A, and a triode, the W.E. 437A. All three types are used in the line and office amplifiers. The new tubes make possible a substantially higher level of broad band amplifier performance compared to their predecessors. They represent the result of improvements made by applying well known basic principles through new tube-making techniques. These techniques have been developed largely within the framework of existing conventional telephone tube manufacturing methods. The development of special, small, low power vacuum tubes for high frequency application in the Bell System began in 1934. The tube program was instituted originally as part of a research project in the field of radio communications. When the development of the LI Coaxial System began it was recognized that similar tubes would be needed. Part of the tube development effort was therefore directed toward the coaxial requirements. Work on the W.E. 384A and W.E. 386A tubes used in the LI system was completed in 1939 as an outgrowth of this program. The demand for amplification over wider frequency bands resulted in further development work along the same lines.