Electron Tubes for the SD Submarine Cable System

Three codes of electron tubes have been designed and developed specifically for use in the SD submarine cable system: the 455A-F, 456A, and 458A. The 455A, B, C, D, E, and F are pentode-type amplifier tubes manufactured as one type and subsequently designated for the six amplifier sockets to obtain optimum repeater performance. The 456A is a gas-filled cold cathode tube used as a power bypass device to (1) protect the heaters of the amplifier tubes, and the low-voltage components in parallel with them, from transient high-voltage surges on the cable and (2) to provide a continuous path for the cable current in case of an open heater in any of the amplifier tubes. The 4">8A signal path protector is a high-speed gas-filled cold cathode tube used at both the input and output of the repeater to protect the transmission path from voltage surges. For a period of approximately two years engineers of the Western Electric Company were resident at Bell Telephone Laboratories to participate in the final development stages of the tubes. As a result of 1311