Vacuum tubes for submerged repeaters

The cost of an interruption in service and of replacing a submerged repeater in a multi-channel telephone submarine-cable system places high importance on the reliability of all parts of such repeaters and particularly on the valves used in them. Thus in this article reliability aspects are stressed. The required properties of valves used in submarine repeaters are first briefly outlined. The fundamentals of design and construction of these valves are then described in general form. An historical survey of seven valves (six pentodes and one, tetrode).introduced between 1947 and 1960 that were concerned in the described investigations is given, and their characteristics are tabulated. The underlying principles involved in the design of the manufacturing section where the valves are made are discussed. A graph and a histogram showing variations of trans-conductance with life and with number of valves are given. A brief appendix shows how the probability of breakdown of a typical repeater system is calculated.