Electron tube life and reliability — Built-in tube reliability

The relationship between reliability and performance ability of tubes, as both are affected by design factors, can be stated with considerable accuracy. For example, a tube with double the mutual conductance of another tube has grid-cathode spacing all other dimensions in the grid vicinity reduced to 59.5 per cent, which may adversely affect microphonic response by a factor of eight. Over the fifteen years from 1930 to 1945, the Gm of tubes was increased at a remarkably uniform rate of 2.18 times (a multiplying factor) every five years; it dropped to 1.19 times for the next five years, and since 1950 there has been no multiplying factor. The reasons for this change of trend in tube design are analyzed as related to fundamental design factors. It has shown that the current practice of using high performance tubes almost exclusively has all but brought about the disappearance of lower performance tubes. Equipment designers could enjoy a consideralbe increase in built-in tube reliability if the newer materials and techniques that have been developed for the high-performance tubes were incorporated in more conservatively designed, lower performance tubes. As affected by design, built-in reliability of a tube decrease much more rapidly than built-in performance increases. The need for better electron tube life and reliability increases in importance year by year. Although effort on reliability development also increases at a rapid pace, the need for even more such development remains a step ahead of the results obtained. This stiuation is due to the ever increasing complexity of electronic equipments. In fact, each accomplishment of a higher degree of reliability extends tube usage into even more demanding applications. The reliability program is thus a dynamic one, and has no presently definable objective level