Abstract :
The first transatlantic, Alaskan, and Hawaiian Submarine Telephone Cables are provided with repeaters spaced about 37.5 miles apart. Each repeater consists of a 3-stage electron tube amplifier and contains approximately 60 components. Because of their inaccessibility for repair or replacement, it is desired that these systems operate for the order of 20 years without failure of any component. This requires a degree of reliability for both active and passive components orders of magnitude higher than are achieved in more conventional systems. Electron tubes and high-voltage capacitors subject to "wear out" have been the subject of intensive development and life testing for more than 15 years. These studies indicate that at the low cathode temperature and low cathode current density used in the electron tubes, satisfactory thermionic performance can be expected for more than 20 years. Likewise, tests on the high-voltage capacitors indicate that, in spite of the use of a high dielectric stress, the probability of a wear-out failure in 20 years is low. These estimates, however, do not include the probability of catastrophic or sudden failure of the components. Since practicable test programs cannot measure the extremely low catastrophic failure rate expected of these components, it must be attained through the use of 1) reliable types, 2) close control of raw materials, 3) simple designs which are easy to make and inspect, 4) careful manufacture, and 5) thorough inspection. This procedure is restrictive and involves close attention to all details in both design and manufacture. Consequently, unusually detailed specifications were required for raw materials, processes, and components. Complete records of all operations and inspections were kept to insure against omissions or errors. Specially selected operators were trained; and required to demonstrate ability to produce satisfactorily before going on production work. Manufacture was carried out under exceptionally clean conditions. The product was inspected at each stage of manufacture so that hidden defects would not be missed. The resulting slow and painstaking manufacture disclosed many defects which would have been overlooked in normal production. Although no numerical value can be attached to the- degree of reliability attained, experience in production and service to date indicate that it is unusually high. Over 270 million component hours of service without a failure have been accumulated to date, which indicates, with 90 per cent certainty, a failure rate of less than 1 in 10,000 per year.
