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BELL SYSTEM TECHNICAL JOURNAL 



element of this type of repeater. It is a small glass bulb with a 

 vacuum that is as good as is practicable to obtain. In the tube 

 is a filament which is heated to incandescence during operation, 



Recei ving Circuit — ^ J ( ^ TransmiUmg Circ ml - 



Fig. 21 — Vacuum-Tube RepeaLcr dement 



and a grid and plate. The circuits directly associated with the tube 

 are shown in more detail in Fig. 21, and this would constitute a device 

 for amplifying currents from one direction. As is well understood, 

 any change in the potential impressed on the grid causes a change in 

 the current flowing in the plate-filament circuit. To obtain complete 

 two-way repeater action two of these amplifier arrangements are 

 combined with the circuits shown in Fig. 22. 



dM Coil -«i-,M 



Fig. 22 — Two-Way Vacuum-Tube Repeater Circuit 



It will be noted that the line circuit from one direction, for instance, 

 the one designated "line west," is connected through a three-winding 

 transformer to a balancing network which is so made up as to balance 



