Reliability of Electron Tubes in Military Applications

Study by Aeronautical Radio, Inc., of electron tubes removed from military equipments, discloses four principal contributors to tube failure or removal: Maintenance and operating conditions, environment, application, and basic tube weaknesses. Examples of trouble caused by misapplication and environment are presented. Over-all returns from various military bases show that one tube in every three removed is not defective and should not have been removed. Taking into account the "no-defect" removals and gradual deterioration failures which could have been detected by good maintenance procedures before they caused equipment failure, only one tube in six removed is of a type liable to produce equipment malfunction. These facts point to shortcomings of maintenance in the face of increasing equipment complexity, and emphasize the urgent need for equipments designed for simplicity of operation and servicing. Laboratory analysis by Cornell University indicates that high-operating temperature is the predominant basic cause of deterioration failures resulting from emission poisoning, interface, and leakage due to sublimation. Heater burnout and heater-cathode shorts, the principal types of catastrophic failures, are traceable to highheater operating temperature. Early results of ARINC tests on improved receiving-type tubes indicate a removal rate only one-third to one-fourth that of their prototypes, which show a rate between one and three per cent per hundred hours of operation. Correction of tube weaknesses appears to lie in diligent application of solutions which are already known. The improvements must be maintained by rigid quality control of the product and continuous sampling of failures occurring under actual operating conditions.