TOLL SWITCHBOARD NO. 3 



23 



ward, or through positions. This feature not only effects a saving in 

 equipment but saves the space in the face of the switchboard which was 

 formerly occupied by the transfer keys. 



Use of Positional Circuit 

 Another circuit feature of the No. 3 switchboard which marks an 

 improvement over switchboard No. 1 is the use of a so-called positional 

 circuit in which is located much equipment such as splitting keys, 

 dialing keys, etc., which heretofore were individual to each cord. 

 Under normal conditions the tip and ring conductors of the front cord 

 are connected to the tip and ring conductors of the corresponding 

 back cord with no shunts across the circuit. This is illustrated in 

 Fig. 6. By the operation of the talking key associated with each cord 



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Fig. 6 — Schematic: Toll cord talking circuit ; talking key normal for toll switchboard 



No. 3 



circuit, the positional circuit is connected between the front and back 

 cords and the operator's telephone set is connected across the circuit 

 as illustrated in Fig. 7. With the talking key of any cord operated, the 

 operator may 



{a) Dial on either the front or the back cord. 

 {h) Split the talking circuit between the front and the back cords. 

 (c) Transfer an inward call from the inward to the outward or the 

 through positions. 



Fig. 7 — Schematic: Toll cord positional circuit; talking key operated for toll switch- 

 board No. 3 



