572 



BELL SYSTEM TECHNICAL JOURNAL 



to resonate with the grid-plate capacitance. For ease of adjustment a 

 somewhat lower fixed inductance may be used and tuned by the ad- 

 justment of a small variable condenser in parallel. This form of 

 neutralization is commonly referred to as "coil" neutralization. At 

 ultra-high frequencies where unavoidable inductances are already 

 present in the form of lead inductances, this "coil" scheme possesses 



100 

 80 



60 

 50 

 40 



30 

 20 



< 



? 10 



I- 

 3 8 



Q. 



H 



8 6 



5 

 4 



100 200 300 500 1000 2000 3000 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 6 — Comparison plot of the outputs of the double-lead tubes and of commercially 



available tubes. 



outstanding advantages over the more usual "capacitance" schemes. 

 These advantages become even more pronounced with the availability 

 of the double-lead tube. 



Verifying this analysis, a "coil- neutralized" two-stage amplifier 

 using two of the largest size tubes was found to yield an output of 60 

 watts at 144 megacycles for Class B operation. Stability, distortion, 

 and band width were quite comparable to the results obtained on a 



