1228 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



methods of checking microphonism in tubes. The industry, in collabora- 

 tion with the Services, is now engaged in standardizing on automatic 

 tappers. The prime requisites for such tappers are: (a) their shock output 

 must be reproducible and must fall within definable limits, (b) their 

 operation cycle must not adversely affect the time required for perform- 

 ing tap tests, and (c) the results obtained must have some relation to the 

 environmental requirements for the tubes. This last condition is, perhaps, 

 the most difficult to attain considering the diverse conditions encoun- 

 tered by tubes in various equipments. 



Of the many tappers devised and employed by the industry, the use 

 of only two are at present approved in the MIL-E-IB specifications. 

 One is a manually operated cork mallet. This mallet is still retained in 

 spite of its shortcoming, for lack of better devices. The second is the 

 General Electric Automatic Tapper, specified for checking microphonism 

 of some of the reliable tubes. This is a motor driven tapper which sub- 

 jects the tube under test to damped low "g" vibrations at the rate of 2 

 taps per second. The tapper and associated circuits are fully described 

 in the MIL specifications. 



Space does not permit the discussion of other proposed tappers or test 

 methods. Two rather interesting papers are listed in References 13 and 

 14, which illustrate the problems involved in the development of suitable 

 devices for checking microphonism in tubes and describe some of the 

 various methods of approach. 



SUMMARY 



The rapid growth of electronic equipment development during the 

 late war has continued with the ever increasing new applications to both 

 military and civilian purposes. It is realized that this growth has placed 

 more stringent requirements on the mechanical characteristics of electron 

 tubes. In order to define intelligently tube requirements, the nature of 

 the disturbances to which tubes may be subjected must be known. It 

 was pointed out that merely applying equipment requirements to the 

 tubes, is not very realistic, since the shock and vibration patterns may 

 be vastly modified by the equipment structures. 



With the help of the recent development of light weight accelerometers, 

 it is now possible to investigate the disturbances at the tube sockets. 

 Both the Industry and the Services have begun to utilize these instru- 

 ments to collect this information. The benefits derived from this work 

 will enable the equipment and tube designers to formulate more accurate 

 requirements and to devise test gear that will simulate more closely field 

 conditions to check on tube quality. 



