Historical Technology Books - 75 in a series - Vacuum Tube Manual: Tomer 1960 Getting the Most Out of Vacuum Tubes (1960)
The purpose of this book is not to add another volume to the many excellent ones available on what makes the vacuum tube work. Rather, it is intended to shed light on the almost completely neglected subject of why these versatile devices sometimes do not work.
Informed scientists and engineers have frequently stated that the life of a vacuum tube in normal service should exceed 5,000 or even 10,000 hours. The fact that some of them do not last this long is well known. The question then is, "Why do they so often give less than their predicted or possible potential?"
J. M. Bridges, Director of Electronics, Office of the Assistant Secretary of Defense, speaking before the RETMA (now EIA) "Symposium on Reliable Applica- tions of Vacuum Tubes" at the University of Pennsyl- vania in May 1956, said: "It has been demonstrated by service tests that the average number of tube failures per operating hour in two equipments of equal complexity, having approximately the same tube complement, can differ by as much as a factor of ten, due entirely to dif- ferences in the thoroughness and completeness of engi- neering design."
If the failure rate of tubes in military equipment can vary as much as ten to one because of circuit design alone, what influence do maintenance practices have on over-all reliability and failure rates? For an answer to this, we refer to Aeronautical Radio's General Report, Number Two, on "Electronic Reliability in Military Applications," July 1957, which states: "All available evidence indicates that this factor — the influence of maintenance personnel — is one of the dominant causes of unreliability in mili- tary equipments." Later in this same report we read, "The conclusion was reached that about one out of every three tubes removed from military equipment was a 'good tube.' "
What can we deduce from all this?
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- Topics tube, tubes, cathode, voltage, grid, current, heater, emission, characteristic, circuit, plate current, tube testers, vacuum tubes, vacuum tube, tube types, tube failures, grid emission, tube tester, tube life, heater voltage