ELECTRON TUBE PERFORMANCE 



317 



The Parabolic Pentode Amplifier 



Over the straight portion of the g-e curve the following relations hold for 

 an input v = P cos pi. 



The fundamental current is Ip = GP where P is the grid swing. 

 The second harmonic current is 



f2p 



1 Ag^ 

 4 Ae 



TYPE 6AG7 

 PLATE VOLTS 300 

 SCREEN VOLTS 300 

 GRID-BIAS VOLTS 10.6 



GRID VOLTAGE, e 



Fig. 1 — g-e characteristic having principally second order modulation over part of the 

 range. 



To find the level H2 of the second harmonic below the fundamental, 

 prolong the straight portion of the characteristic down to the virtual cutoff 

 £0 (Fig. 1). Then 



H, = 20 log "f 



20 log ^Sr^" + 12. 



For the case when all of the parabolic characteristic is used 



P = ^ and F2 



20 log ^ + 18. 



If it is desired to express Ih in terms of the output current ip and the 

 space current I'o the following approximate formula may be used: 



Hi = 20 log J + 18. 



