THERMIONIC VACUUM TUBES 



87 



be obtained. Introducing certain approximations this expression 

 may be written, 



1 



ipi(R+Ro) = 

 1 



V2 



E 



p> 



(14) 



in which terms of the order — are neglected in comparison to unity. 



M _ 



i p i is the fundamental component of the space current, E p is the mean 

 plate voltage and the term R is largely determined by the tube, and 

 while not generally equal to r p , is apparently not much different from 

 it. This equation indicates that the amplitude of oscillation is prac- 

 tically independent of the value of m- 



The remarkably simple relation given by Equation 14 has been 

 tested for a wide variety of circuits and tubes and has been found 

 to hold with a very fair degree of accuracy. It may safely be taken 

 as indicating quite approximately what response may be expected 

 from any tube and circuit when operated at a particular applied E p . 

 The equation is likely to be more closely followed the more carefully 

 the adjustment of circuit for maximum efficiency has been made. 



The condition E e 



= E, 



should not be considered as invariable. 



Adjustments can readily be made for which E gmax will either be ap- 



EE? 



5000 «000 



Attaches Impedence -0HK6 



Fig. 5S 



preciably less or greater than E Pm - m . It is generally found how- 

 ever that these adjustments do not give the most efficient operation. 



Additional information as to the relation between the amplitude of 

 oscillation and certain circuit constants are given in Figs. 58, 59, 60, 

 61. Fig. 59 shows that an oscillator tube may present a well-defined 

 condition of temperature saturation. Figs. 60 and 61 show that the 

 value of the feed-back voltage and grid leak resistance r g may be 

 varied within wide limits without affecting the output markedly. 



49. Efficiency. The efficiency of an oscillator may be defined as 

 the ratio between the energy of oscillatory current and the d.c. energy 

 supplied to the plate circuit. This leaves out of account the energy 



