ELECTRON TUBES FOR A COAXIAL SYSTEM 1123 



The gain-band performance in this repeater, or in any other circuit, will 

 be less than that shown in the curves in Figs. 2-4 since the total shunt 

 capacitances in a working circuit are always larger than the cold tube 

 capacitances used in calculating the inherent figure of merit. 



3.4 Test Specifications 



The test specifications for the L3 tubes were written with the L3 system 

 requirements as the prime consideration. In addition to the usual tests made 

 on small tubes, a modulation test was included for the 435A and 437A 

 tubes because of the importance of this characteristic in terms of system 

 performance. In order to avoid penalties which can result from unwanted 

 systematic deviations which pile up in a long system, requirements have 

 been set up which will control the distribution of transconductance, modula- 

 tion, and some of the most critical interelectrode capacitances. By the 

 application of suitable quality control methods, it is expected that these 

 requirements can be met economically and that such measures will prevent 

 the manufacture of large numbers of tubes having average characteristics 

 far off the design values. When simple go, no-go limits are used, it is not 

 economical to set close enough limits to attain the desired control of the 

 average characteristics. 



4. Conclusions and Future Possibilities 



The fundamental problem in the development of repeater tubes for 

 broad band coaxial systems has been to devise means for utilizing closer 

 and closer grid-cathode spacings without sacrificing life performance. 



The closer spacings have been made possible by devising rigid control 

 grid supporting structures which can be wound with very small diameter 

 wire. The wire is held under tension by the supporting frame so that a flat 

 winding is produced which can be spaced very close to a flat cathode. 



The possibilities for the development of tubes which will provide still 

 better broad band amplification depend to a great extent upon the kind 

 of system design to be considered. If higher figure of merit, as defined in 

 this article, can be utilized, considerable improvement can be realized with 

 space charge controlled tubes such as the 435A, 436A and 437A by using 

 mounting arrangements which provide more precise means of establishing 

 and maintaining the critical dimensions. 



Acknowledgements 



Several members of the technical staff and their assistants have con- 

 tributed materially in solving the numerous technical problems which arose 

 during the development of these tubes. In addition, those who fabricated 



