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BELL SYSTEM TECHNICAL JOURNAL 



Fig. 9. Three stages with impedance coupling are used and the feed- 

 back circuit is connected between the plate circuit of the last tube and 

 the grid circuit of the first. The amount of gain and the slope of the 

 gain -frequency characteristic are controlled by the condensers and 

 line equalizer in the feedback circuit. 



EQUALIZER 

 IN FEEDBACK 



TUBE-TESTING 

 JACKS 



GAIN- 

 REGULATOR 

 CONDENSER 

 GAIN-CONTROL 

 CONDENSER 



REVERSIBLE 



SYNCHRONOUS 



RECEIVER MOTOR 



DIAL INDICATES 

 "POSITION OF REG- 

 ULATOR CONDENSER 



Fig. 8 — Line amplifier. 



RECEIVER 

 MOTOR 



/ER 1 \ 



LINE 

 EQUALIZER 



TO FLAT-GAIN 

 MASTER CONTROLLER 



- FLAT-GAIN 

 REGULATOR 

 CONDENSER 

 (14 DB RANGE) 



FLAT-GAIN 



CONTROL 



CONDENSER 



(10 DB RANGE) 



! + 



Fig. 9 — Schematic of line amplifier. 



The line equalizer has the same attenuation slope as the line. In 

 the introduction of this equalizer in the feedback circuit careful atten- 

 tion to phase shift requirements was required. Four types of equalizers 

 are available, for different repeater spacings, to compensate for the 

 cable distortion which occurs at a temperature of 55° F., additional 

 means being provided to compensate for variations which occur as the 

 cable temperature swings away from this value. The solid curve of 

 Fig. 10 shows a repeater gain characteristic with one of these equalizers 

 in the feedback circuit. 



