Design Factors of the Bell Telephone Laboratories 1553 Triode 



By J. A. MORTON and R. M. RYDER 



(Manuscript Received Aug. 3, 1950) 



TN DEVELOPING microwave relay systems for frequencies around 

 -■■ 4000 megacycles, one of the major problems is to provide an amplifier 

 tube which will meet the requirements on gain, power output, and dis- 

 tortion over very wide bands. As the number of repeaters is increased to 

 extend the relay to greater distances, the requirements on individual 

 amplifiers for the system become increasingly severe. A tube developed 

 for this service is the microwave triode B.T.L. 1553, the physical and 

 electrical characteristics of which were briefly described in a previous 

 article.' In the development of such a tube, both theoretical and ex- 

 perimental factors are involved; illustration of these factors in some 

 detail is the purpose of the present paper. 



Ciiven the application, a number of questions arise at the outset. What 

 determines the tube type — why pick a triode for development, rather than 

 a velocity variation tube, or perhaps a tetrode? What electrode spacings 

 are necessary in such a tube, and what current must it draw? How is its 

 performance rated, and how does it compare with other tubes? To what 

 extent can the performance be estimated in advance? What experimental 

 tests can give more precise information? Some answers to these questions 

 were obtained by the use of figures of merit, which led up to the choice of 

 a triode as most promising for development, and which also led to the 

 subsequent method of optimizing the design for the particular system 

 application of microwave amplifiers and modulators. 



The design process may be said to proceed by the following series of 

 steps: 



1. Formulate the system requirements, frequently with the aid of one 

 or more figures of merit. The purpose here is to concentrate attention 

 upon the limitations inherent in the tube alone by eliminating considera- 

 tions of circuitry or of other parts of the system. The figure of merit 

 measures tube performance in an arbitrary environment, so chosen as to 

 be simple, and also directly comparable to the actual system requirement. 



2. Make tentative choices of tube type, and analyze further to find out 



' J. A. Morton, "A Microwave Triode for Radio Relay," Bell Liboralories Ricord 27, 

 166-170 (May 1949). 



496 



