Life of valves with oxide-coated cathodes

Discusses the life of special valves for telephone repeaters made by Standard Telephones & Cables Ltd. Valves may be divided into three classes, short, medium and long lives. The short-lived valves (a few thousand hours) suffer from design faults which are well recognized. In the medium class (2 000-10 000 hours) failure is often due to interface resistance. The long-life class (10 000-50 000 hours) are those in which the ratio gm/cathode area is small. Interface resistance build-up is described in some detail and the conclusions for the equipment designer discussed.