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BELL SYSTEM TECHNICAL JOURNAL 



negative grid triode in some respects offers greater theoretical difficulty 

 than does the positive grid triode, which is treated in the next section. 

 However, because of the greater ease in the interpretation of the re- 

 sults in terms which have become familiar through years of use, the 

 negative grid triode is treated first. 



too 



I To I 



0.20 



0.10 



-5 < 



Fig. 3 — Magnitude and phase angle of plate impedance of diodes or of 

 negative grid triodes versus transit angle. 



In the analysis recourse must be had to approximations and ideali- 

 zations which allow the theory to fit the practical conditions. In the 

 selection of these, the first thing to notice is that no electrons reach 

 the grid, so that most of the electrostatic force from the grid acts on 

 electrons quite near the cathode, where the charge density is very great. 

 The most prominent effect of a change in grid potential will thus be a 

 change in the velocity of electrons at a point quite near the cathode. 

 It will thus be appropriate to assume as a starting point that the 

 alternating-current velocity at a point Xi, located quite near the 

 cathode is directly proportional to the alternating-current grid poten- 

 tial, Vg, so that we may write, 



when 



£/i = (M + iN) = k Vg. 



(30) 



