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BELL SYSTEM TECHNICAL JOURNAL 



resistive branch and they are both in series with the effective generator 

 o-gp, whereas in the classical picture the capacity branch shunts the 

 effective generator and plate resistance which are in series with each 

 other. Practically the difference between the two equivalent circuits 

 is negligible except at extremely high frequencies. The following 

 physical viewpoint supports the newer picture. 



Fig. 7 — Magnitude of complex mutual conductance of negative 

 grid triodes versus transit angle. 



As pointed out, the action of the grid is exerted mostly on the region 

 of dense space charge existing very near the cathode and variations 

 in the grid potential act on the velocities of the emerging electrons, 

 thus producing the equivalent generator of the plate circuit. The 

 plate current consists of conduction and displacement components 

 whose sum is the same at all points in the cathode-plate path. Near 

 the cathode, the conduction component comprises the whole current 

 because of the high charge density and the effective generator acts in 

 series with this current and hence in series with the path of the dis- 

 placement current into which the character of the total current gradu- 

 ally changes as the plate is approached. 



Strictly speaking, the equivalent circuit corresponding to (32) ex- 

 ists, not between the plate and cathode, but between the plate and 

 the potential minimum near the cathode which is caused by the finite 



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