ACCELERATION EFFECTS ON ELECTRON TUBES 1215 



Particular attention must be paid to the design of the filters since these 

 elements are apt to introduce excessive phase shift and oscillations. A 

 variable frequency electronic filter has been found to be quite serviceable 

 due to its flexibility in the choice of cut-off frequencies. 



Additional information on shock and vibration instrumentation is 

 given in Reference 5. Since the presentation of mechanical distrubances 

 is, to some extent, limited by the transducers and their associated cir- 

 cuits, there is a trend towards a certain amount of standardization of these 

 components so that results can be compared on an industry wide basis. 



TUBE DESIGN PROBLEMS IMPOSED BY ENVIRONMENTAL CONDITIONS 



It follows from the numerous acceleration measurements made at the 

 installation points of equipment, that electron tubes, together with other 

 components, have to withstand a large variety of conditions. Without 

 over-simplifying the problems involved, it is perhaps permissible 

 to divide these disturbances into two classes : ballistic shock, and transi- 

 tory or sustained low g vibrations. Although, as a first approach, the 

 effect of these distrubances on tube elements may be probed by mathe- 

 matical analysis, the final design must be proven in by laboratory tests 

 under controlled conditions. In discussing the influence of shock and vi- 

 bration on tubes, their elements are frequently presented schematically 

 as cantilevers, Fig. 8(a). While this assumption is a close approximation 

 for some of the older tubes, such as the Western Electric No. 349B tube, 

 Fig. 8(b), most tubes of later design. Fig. 8(c), do not lend themselves 

 to such simple analysis due to their more complex structure. The response 

 of elements to even simple shock pulses on tube envelopes are influenced 

 by factors such as the clearances in micas, mica fits in the bulbs and tight- 

 ness of mount assemblies. 



It is obviously beyond the scope of this paper to analyze the destruc- 

 tive effects of shocks and vibrations on equipment. A few of the many 

 excellent articles and publications on this subject are listed in Reference 

 6. It is equally impossible to present all of the many problems facing the 

 electron tube engineer in designing tubes that will reliably serve their 

 purpose under adverse conditions. Since tubes must be designed to with- 

 stand distrubances encountered in the field or be adequately protected, 

 the following notes, highlighting some of these problems, will be of in- 

 terest to equipment as well as tube engineers. 



Influence of High g Shocks 



In certain applications, tubes are required to withstand occasional 

 high shocks such as those produced in military applications by explosions 



