The life of repeater tubes and its testing methods

A report on the life of repeater valves in use at present, the stability of their characteristics and the methods of testing them. Examination proved that the main causes of breakdown were (a) air leakage at the stem and (b) drop in cathode activity. To investigate (a), the electrolytic current flowing at the stem was measured and its variation when the valve was running checked. This was followed by research into the most suitable stem glass and consideration of an accelerated-life test procedure. It was found that defect (b) could be studied by means of an accelerated life test involving overheating. The life tests were studied statistically.