Mechanical vibration of vacuum tubes

Since the beginning of the art of vacuum tube building, vacuum tube engineers have been faced with many mechanical problems as well as electrical problems. Early mechanical problems were comparatively small because most of the tubes were used in stationary apparatus where little or no vibration was envolved. As time went on, vacuum tubes were placed in portable equipment and this useage established the need for a tube that was mechanically strong enough to give reliable electrical behavior where the tube was subjected to considerable vibration…. Recently it has been shown that vacuum tubes operating in the instrument cabins of jet-powered aircraft have shown malfunction in flight because of the very high levels of sound vibration which the tube is subjected to. Since this vibration condition caused by jet turbines and other moving apparatus of aircraft causes problems in tube failure and circuit misbehavior, the author became interested in the measurement of unwanted internally generated voltages in these vacuum tubes that were caused by the vibration of the tube elements when the tube operates under mechanical vibration. To be able to utilize the findings of such an investigation it was felt desirable to establish a term in the equivalent circuit of the vacuum tube which would represent the internally generated voltages when the tube is operated under a given range of mechanical vibration frequencies. When this equivalent circuit is established for a given tube type, allowances for these voltages can be made in designing the circuitry that goes with the tube. Also it is of particular interest to observe the effect on the normal output voltages that this new term has and establish a means of finding out the components or the output voltage which can be attributed to the mechanical vibration. Knowing these things, circuit designers who are designing circuits for airborne and other equipment that is known to operate under vibration will be able to calculate more workable designs with fewer malfunctions --Introduction, pages 1-2