STABILIZED FEEDBACK AMPLIFIERS 



13 



have been tested where the number of stages ranged from one to five 

 inclusive. In every case the feedback path was from the output of 

 the last tube to the input of the first tube. 



10 20 30 40 



OUTPUT OF FUNDAMENTAL- MILLIAMPERE:S INTO 600 OHMS 



50 



Fig. 7 — Modulation characteristics with and without feedback for the amplifier of 



Fig. 2. 



Experimental Results 



Figures 6 and 7 show how the gain-frequency and modulation char- 

 acteristics of the three-stage impedance coupled amplifier of Fig. 2 

 are improved by negative feedback. In Fig. 7, the improvement in 

 harmonics is not exactly equal to the db reduction in gain. Figure 8 



