7. PREDICTING TUBE PERFORMANCE
8. TUBE TESTERS
10. METHODS FOR LENGTHENING TUBE LIFE
11. Glossary
The purpose of this guide 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 Applications of Vacuum Tubes" at the University of Pennsylvania 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 differences in the thoroughness and completeness of engineering 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 military 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? It appears possible that more effective maintenance practices can in some instances, reduce over-all tube failure rates by as much as 90%. Extensive military records, covering thousands of tubes in all types of electronic apparatus all over the world, have shown that these results are entirely possible.
It is for the purpose of pointing out those engineering practices leading to premature tube failures, and those maintenance practices contributing to additional failures, that this guide is written. I hope that, as a result of this knowledge, those responsible for the maintenance and servicing of home entertainment, business, industrial, and military equipment will gain a new appreciation of vacuum tubes, so they can obtain greater satisfaction from them in the future.
Vacuum Tubes--The Important 4/5ths of Electronic Circuits
Over 80% of all electronic equipment defects result, directly or indirectly, from tube failures. Why do tubes fail? What can be done to prevent them from failing before their time? How can you determine whether a tube is good or bad, or how well and how long it will work in a given circuit? Should tubes be replaced periodically, whether they've failed or not ... or should they be tested every so often, and replaced if indications show them to be below par? This guide supplies the answers to these profound questions ... plus many, many more.
Like Watching a Play From Backstage Author "Bud" Tomer, an international authority on tubes, is well-known for his candid "Tech Tip" bulletins and his slide-film presentations to service, military and engineering groups. Within these covers you'll find a virtual encyclopedia on vacuum tubes--yet the author has not delved into mathematical details that would be of interest to only a few tube engineers. Everything is focused toward the interest of those who use tubes--either for replacement purposes or in original equipment designs.
In his refreshing, down-to-earth style, Mr. Tomer sheds a bright light on such areas as, "Why so many tube types?" "What About Tube Testers?" etc.
Other Interesting and Informative Subjects Include ...
• 10 reasons why tubes fail
• Predicting tube performance
• Selected and premium tubes
• Lengthening tube life
Anyone who has anything at all to do with electronic equipment-whether he is responsible for maintenance, design, or proper use should read this guide. It is written for the benefit of service personnel who repair and maintain consumer goods such as radio, TV, and hi-fi equipment-or industrial equipment used in production and manufacturing processes--or even military equipment such as missiles, satellites, computers and radar gear.
It also will be of use to engineers and technicians who design any of this equipment, as well as for those who use it.
You'll Also Learn About:
• Catastrophic failures--what they are, when and why they are most likely to occur.
• Degenerative failures--what happens to tubes over a period of time.
• Subjective failures--why a seemingly nor mal tube fails to work in certain applications.
• Characteristic variables-differences that may exist between tubes of the same type.
• Special-purpose tubes--considerations for filamentary, low Ep, photo tube, voltage regulator and thyratron types.
ABOUT THE AUTHOR
ROBERT B. TOMER, or "Bud" as he is known throughout the industry, has literally pulled himself up by his own bootstraps. Starting as a helper in a radio store, Bud progressed to test equipment builder, laboratory technician, production foreman, design engineer, chief engineer, director of industrial engineering, and director of commercial engineering.
Today he is manager of field engineering for CBS Electronics, and a recognized authority on tubes, transistors, and a number of other subjects. Born in Springfield, Massachusetts, Bud (like many others during the Depression) was forced to forego his formal education. In his own words: "My first major contribution to science was a reaffirmation that you must eat to live. I lost out in an attempt to prove otherwise!" Still, his profound knowledge is quite diversified (he holds several patents in photography and color television and, since 1932, has held a ham license with call letters WlPlM) . Since 1944 his articles have appeared in numerous trade journals. In addition, he has published twelve papers on engineering and ham topics, is author of CBS Electronics' "Tech Tips," and has written ten major engineering bulletins on tubes and transistors. He also is co-author of the CBS Electronics Transistor Home Study Course.
Most service technicians know Bud from his lectures, which he has conducted before more than 20,000 people in the past three years. He illustrates his lectures with slides he prepares himself, including the photography and sound. Copies of these slide talks have been presented by others to another 150 to 200 audiences, bringing the total who have heard his lectures to over 40,000.
Also see: Designing and Building Vacuum Tube (Valve) Amplifiers