STABILIZED FEEDBACK AMPLIFIERS 



15 



50 



0.1 



05 



I 5 10 



FREQUENCY IN KILOCYCLES 



?^ 

 Q 

 LJ UJ 

 Ul UJ 

 Zli. 



< 



m5 



DB CHANGE IN GAIN WITHOUT FEEDBACK 

 -.2 +.2 



+ .005 



-j005 



50.010 



50.005 z 

 < 



a. 

 50.000 y 



49.995 



24-0 245 250 255 260 



PLATE BATTERY SUPPLY VOLTAGE 



Fig. 9 — Representative gain stability of a single amplifier as determined by 

 measuring 69 feedback amplifiers in tandem at Morristown, N. J. 



The upper figure shows the absolute value of the stability index. It can be seen 

 that between 20 and 25 kc the improvement in stability is more than 1000 to 1 yet 

 the reduction in gain was less than 35 db. 



The lower figure shows change in gain of the feedback amplifier with changes in 

 the plate battery voltage and the corresponding changes in gain without feedback. 

 At some frequencies the change in gain is of the same sign as without feedback and 

 at others it is of opposite sign and it can be seen that near 23 kc the stability must 

 be perfect. 



