THEORY OF MVLTI-ELECTRODE VACUUM TUBES 



61 



is imposed by circuit coupling requirements and sometimes by restric- 

 tions on the permissible harmonic content in the power output. This 

 limitation results in an amplification ratio that is much smaller than 



1600 

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 400 

 200 



1.8 



§1.4 



Z 1, 



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2 

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if) 



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< 



-10.' 



0.2 



800 

 1600 

 1400 

 1200 

 1000 

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 600 

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-9 -8 -7 -6 -5 -4 -3-2-1 1 2 



CONTROL GRID VOLTS, Eg 



Fig. 6 — Amplification factor, transconductance, and plate resistance of a screengrid- 

 tetrode as functions of the control-grid voltage. 



the amplification factor; but even so, a considerably higher amplifica- 

 tion ratio usually can be obtained than with triodes. This is apparent 



