Getting the most out of Vacuum tubes

Book excerpt: Types and causes of tube failures, what to expect from tubes, testing methods, and all about tube maintenance programs. 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 there 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 book supplies the answers to these and many many more questions!