902 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



0.3 0.4 0.5 0.6 0.8 1.0 2 3 4 5 6 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 13 — Regulation error per one db regulation. 



8 10 



regulating network, but the final values of the elements represent a long 

 process of incorporating secondary corrections as our knowledge of the 

 amplifier grew. Original constraints included the necessity of including 

 as part of the beta circuit not only the relatively large parasitic capacity 

 of the Eimplifier and the coupling network shield to shield capacity, but 

 also the screen resistor and by-pass condenser of the second tube, which 

 as usual is by-passed not to ground but to cathode, for modulation rea- 

 sons. It is also required that the beta circuit have the correct dc resistance 

 to serve as the cathode bias resistor of the second tube, and that it in- 

 corporate provision for metering this bias through suitable decoupling 

 elements which are among the gain-determining elements of the network. 

 Finally, this network was used as the mop-up equalization network of 

 the amplifier, and its element values were readjusted to give the correct 

 amplifier gain after the performance of a representative group of am- 

 plifiers with average coupling networks and tubes had been determined. 

 In doing this tailoring, it is necessary to precorrect for the effects of non- 

 infinite feedback, since the gain of the amplifier is not exactly a direct 

 function of the beta circuit admittance. The configuration of the input 

 beta circuit is shown by Fig. 14; it is a simple two terminal network. Its 

 in-band impedance varies from about 1,000 ohms at 300 kc to 110 ohms 

 at 8.35 mc. 



The output beta circuit is relatively fiat, which in this case is the 

 optimum condition for signal-to-noise and feedback loop stability con- 

 siderations. Because; of this simplicity, it is possible to incorporate in 

 this network provision for adjusting the gain of the amplifier to reduce 

 the misalignment of the system. 



