ACCELERATION EFFECTS ON ELECTRON TUBES 1217 



(d) damage to mica serrations and enlarging of the mica holes which 

 support and space tube elements. The deterioration of the mica is also 

 known to liberate gas, which, in turn, results in a reduction of the 

 vacuum. 



Permanent damage is also caused by deformation of elements beyond 

 their elastic limit. Bowing of grids and cathodes as a result of shock has 

 been reported in some applications. 



Although not always realized by design engineers, shocks and vibra- 

 tions of surprising magnitudes may also occur in handling and shipping. 

 If these conditions are not taken into consideration during the design 

 stage, the over-all cost of the product may be adversely affected by the 

 necessary protection that has to be built into the shipping container to 

 assure safe arrival of the packaged article at its destination. While many 

 factors enter into the proper design of shipping containers, such as mois- 

 ture and corrosion protection, the selection of cushioning materials is 

 perhaps the most important. Since it is desirable from a storage and 

 shipping cost standpoint to keep the package bulk to a minimum, and 

 protective packaging cannot always compensate for design weakness, 

 adequate strength must be designed into the tube even though it will 

 not be subjected to severe shocks once it is installed. A rather complete 

 analysis of the dynamics of package cushioning is given in Reference 7. 

 At present, military requirements specify that packaged tubes must 

 safely withstand several three foot drops onto a hard surface. 



Influence of Low g Disturbances 



In contrast to the relatively infrequently occurring high peak shock 

 and vibrations, we find that many equipments are often subjected to 

 repetitive shocks and sustained vibrations at lower acceleration levels. 

 These conditions are generally encountered in vehicle, ship and airplane 

 applications. Although these shocks and steady state vibrations can be 

 attenuated through the use of shock and vibration mounts, the effec- 

 tiveness of these mounts may be reduced sharply by a change in disturb- 

 ance frequencies from normal. 



Tube failures resulting from these conditions are generally caused by 

 fatigue of some tube elements. For instance, the continual hammering 

 of micas against tube walls or chattering of cathodes and grids in the 

 mica, may reduce the value of the micas as supporting and spacing ele- 

 ments, and since tubes are required to function under these conditions, 

 the gradual degradation of the micas will bring about an increase in the 

 tubes' microphonic output. Where microphonism is a factor, the useful 



