VACUUM TUBE ELECTRONICS 



91 



be to move the curves on Fig. 13 bodily to the right. The lowest fre- 

 quency which will just allow the origin to be included within the loop 

 when the series resistance is reduced to zero and the inductance is 

 adjusted, corresponds to a grid-plate transit angle of lir. 



It must be remembered that the foregoing details apply only to 

 curve A of Fig. 11, and it has already been pointed out that curve A 



Fig. i: 



-Curve A of Fig. 1 1 together with the image corresponding 

 to negative frequencies. 



represents a limit which can be approached in practice, only as the 

 grid capture fraction is made smaller and smaller. Curve B can well 

 be duplicated in experiment. For this case, the lowest frequency at 

 which oscillations may be expected is much higher than before, since 

 the transit angle must be equal to 47r before the resistance becomes 

 negative. Actually, conditions intermediate between the two curves 

 may be realized, so that from a practical standpoint the transit angle 



