938 



~G = 



2nr n La 



1/(1 _ 4j, »„« LCy + 4jr' n' 6' L' * 

 G now becomes a maxiniutu tbr 4.^' ?i* />6'^ 1, ie. it' the circuit 

 (LC) is tuned to the grid potential trequency '). 



u 

 We again tind G„^a^ = - . 



b 



The ainpiification as defined above, has the same maximinn value 



- in any case, so that it indicates a property of the audion. That 

 b 



our detinition is an obvious one, is readily seen in the case one 

 has to do with several audions connected in series. The tension on 

 the resistance or self-induction in the anode circuit of the first 

 audion is connected to the grid of the second and so on. The ratio 

 of the variations in the grid potentials of the two audions is there- 

 fore equal to G, and so will be the ratio of the anode current 

 variations. This latter ratio can easily be measured. Indeed we 

 found the maximum ratio of the anode current variations to be 



a 

 equal to — . 



2. In order to increase the amplifying action of the audion, 



Franklin among others have advi- 

 sed the use of reaction circuits, in 

 which the plate current reacts on 

 the grid circuit, e.g. by magnetic 

 ^ coupling. 



We will discuss now, the charac- 

 teristic properties of the audion 

 that are of importance in reaction 

 circuits and more specially in the 

 case of figure 1.') 



We have assumed that in the 

 secondary circuit a damped vibra- 

 tion is set up, and that the poten- 

 tial on the condenser C^ is of the 



IRSsii 



form 



V =zf[t)=z 70 sin 2jt nt (1— «-,"') «-" 

 In this case we get the following system of equations 



') While in the two previously treated cases, large values of R and L must be 

 used to obtain maximum amplification, here normal L and C' will suffice. 

 ^) See Vallauri loc. cit. fig. 7. 



f* 



