FREQUENCY RESPONSE OF INTERVALVE COUPLINGS 



circuit is Figure 9.18. Consider the behaviour of the network R^CcR^Cin. 



1^2 grid 



If /?£, is small in comparison 



Fout 



Figure 9.18 

 R2IJ0JC 



in 



R.2 + \IJcoCin 



^in R?IJMCin Riljf^Cc 



which simplifies to 



/?2 + ^ I JmC in Ri + l/ywQ 



Kout 



Ro 



in 





Now let 



Cn = ~ 



^in J^2 



^1 



c 



Pentodes direct coupled 



Pentodes 



ac. 

 coupled y 



Pentodes battery 



coupled 

 ^^ 



Pentodes divider coupled 



Tnodes direct 

 coupled 



Triodes divider coupled 



log Frequency ^-♦- 



Figure 9.19 



If this is substituted into the above, we find the bracketed term reduces to 

 unity. Therefore Fout/J^in is merely ^^2/(^2 + ^i)- It is as if there were no 

 capacitance there and the couphng is not frequency conscious. 



What we have done is to arrange that the fraction of the signal transferred 

 from Fi anode to V^ grid is independent of frequency. The upper frequency 



157 



