we find 



MODULATION IN VACUUM TUBES 



Cio = 6oio/(l + Rhm), 

 Coi = 6001/ (1 + Rhxm), 



Ooii -f~ 2i?"doCoi02oo R(-'i)\b\\o RC\(\b\o\ 



449 



Cu = 



in which 



hrst 



1 + i?6ioo 

 1 C J{ll,,}Q, -C,«o' -^''0' 



r ! 5 ! / ! dE/dEn'dEc' 

 and £„o is the fixed potential of the second grid. 



VOLTS PLATE POTENTIAL 



Fig. 2a — Plate resistance as a function of plate potential with grid potential as a 

 parameter. EL tube No. 109,150. // = 1.1 amperes 



We proceed to the methods used for the experimental determination 

 of /x and Ro for the three element tube. 



Measurement of Tube Parameters 



The amplification constant and plate impedance of a three element 

 tube may be measured with precision by a well-known method due in 

 principle to J. M. Miller^ which requires no explanation here. The 

 method as originally proposed is somewhat inconvenient in that the 

 space current of the tube under test passes through a resistance 

 common to the alternating measuring current, so that the operating 



* Proc. I. R. E., Vol. 6. 



