600 BELL SYSTEM TECHNICAL JOURNAL 



this development we may distinguish between two methods of approach. 

 In one the attempt was made to modify the low-frequency network of Fig. 

 5 to include transit time effects to a first order of approximation. ^ The 

 second approach differed in that attention was directed only toward the 

 electron stream itself, while the circuit elements connecting the stream with 

 the physically available terminals were grouped together with the external 

 circuit elements.^ The latter approach represented a particularly useful 

 one from a physical point of view and it also extended the use of basic circuit 

 elements to include the general diode impedance as a new circuit element 

 complete in itself. However, even in this latest approach the four-pole 

 point of view was not adopted, with consequent loss of generality and unity 

 in viewpoint. Moreover, the fact that only the electron stream itself was 

 considered caused some confusion. 



With this brief review of the development of equivalent circuit representa- 

 tion of vacuum tube amplifiers in mind we turn now to the main body of the 

 paper in which a more general treatment of the problem is considered. It 

 will be shown, in the coming sections, how it is possible to lump all the 

 factors involved in vacuum tube amplifiers, i.e., physical circuit parameter 

 and internal electronic effects involving the electron transit time, into a 

 single coordinated picture with an equivalent circuit representation of the 

 overall effect. 



Equivalent Circuit Representation or Active Linear Four-Pole 



Pole Equations 



Whenever the response of a general transducer is related in a linear manner 

 to the stimulus, the transducer behavior is described by two linear relations. 

 Although we are primarily concerned with electromagnetic transducers the 

 concepts to be used are of broader utihty and may, for example, also be 

 applied to mechanical and electromechanical transducers. 



There are various ways in which the behavior of the four-pole may be 

 expressed analytically. The form expressing current equilibrium has al- 

 ready been given and it may well serve as a starting point for the following 

 discussion: 



Thus we have: 



/i = /3iiFi -f /312F2I 



h = iSsiFi H- ^22721 



(14) 



2F. B. Llewellyn, "Electron-Inertia Effects," Cambridge University Press, 1941. 



' F. B. Llewellyn and L. C. Peterson, Interpretation of Ultra-High Frequency Tube 

 Performance in Terms of Equivalent Networks, Proceedings of the National Electronics 

 Conference, 1944. 



