614 



BELL SYSTEM TECHNICAL JOURNAL 



similar set of reciprocal relations between the open-circuit driving-point 

 impedances is also present. 



In regard to the networks it may first be observed that, since they were 

 derived from parameters upon which no restrictions had been placed on 

 either frequency or space charge, they are also generally valid. In passive 

 circuit theory one is accustomed to the use of only the three basic elements 



♦ D 



921 



^^^I 



u -9'* 



(a) 



y2f 



y2i 



>^y22 y 11 922 



yn y22 



(b) 



1 y2i 



' .^922 "911922 



KV, 



(c) 



K=- 



yiiO+i) 



Fig. 21 (a, b, c) — Three forms of equivalent circuits of the grounded plate triode valid 

 at all frequencies. 



of resistance, inductance and capacitance. For the networks now under 

 consideration other quantities also need to be included. However, as 

 normally operated there is usually complete space-charge in the cathode-grid 

 region and a very small amount of space charge in the grid-plate region. 

 Under such circumstances the admittance ^22 is a simple capacitance and the 

 amplification factor /i is a real number. The admittances yn and ^21 , on 

 the other hand, do not allow accepted circuit interpretation to be made, 

 except in the range of moderately low frequencies when electron transit 



