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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



It is interesting to note that the gross non-Hnearities in the vacuum tube 

 plate circuit have their counterparts in the transistor collector circuit. For 

 example, the counterpart of plate current cutoff is collector voltage cutoff. 



The relationship between vacuum tubes and transistors is not only quali- 

 tative, but can be made quantitative as well provided a suitable vacuum tube 

 is chosen for comparison with the transistor. The requirements are that the 

 vacuum tube and transistor have similar dissipation ratings and that /z 

 be equal to a. These conditions are roughly satisfied by the vacuum tube 

 and transistor of Fig. 1(a) and Fig. 1(b). By comparing the axes in these 

 two figures it may be seen that one milliampere in the transistor corresponds 



132 10 20 



MILLIAMPERES 



(d) (b) 



Fig. 1— The static characteristics of a transistor look like those of a vacuum tube triode 

 provided transistor currents are compared with vacuum tube voltages and vice versa. 



to 6.6 volts in the vacuum tube and vice versa. It follows that, in this case, 

 transistor currents are related to vacuum tube voltages through a "trans- 

 formation resistance," r, given by 



6.6 volts 



(1) 



f = 



(10) -3 amps 



= 6,600 ohms. 



Cmcurr Considerations 



The internal structure of a vacuum tube imposes a particular set of re- 

 lationships between the vacuum tube currents and potentials. At low fre- 

 quencies these relationships are given by the static characteristics which 



