1216 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



of some kind. It is generally permissible that, during very severe shocks, 

 electronic equipment is non-operative; therefore, the response of tubes 

 during these disturbances may fall outside of assigned limits. However, 

 since it is highly important that operations resume immediately, the 

 tubes must show no permanent change nor have caused damage to the 

 circuits as a result of temporary faulty operation. Although protective 

 shock mounts are usually employed on equipments exposed to these 

 conditions, damped equipment vibrations excited by the attenuated 

 shock wave are superimposed on the pulse felt by the tube. 



Brittle or stiff tube components are most susceptible to shock because 

 of their inability to absorb the shock energy by elastic deformations. 

 Failures falling into this category are: 



(a) glass breakage, which may be brought about by impact due to 

 excessive movement of the tube or adjacent components during the 

 impact. 



(b) metal to glass seal fractures, produced by shock loads on the tube 

 leads and seals. 



(c) heater or filament failures and opening of welds. 



=3r 



(a) (b) (c) 



Fig. 8 — Electron tube structures: (a) Simplified anode and cathode structure 

 of a Western Electric No. 349B tube, (b) Western Electric No. 349B tube, and (c) 

 typical miniature tube. 



