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BELL SYSTEM TECHNICAL JOURNAL 



line to receive the 20-cycle, or the higher frequency ringing current, 

 and arranging this relay so that it gives the line signal or the cord 

 supervisory signal direct without going through the step of changing 

 ringing frequencies. 



Furthermore, the practice of using 20-cycle current in the cord 

 circuit for linging has been discontinued and ringing is effected in the 

 No. 3 switchboard by connecting 24-volt direct current through the 



^■i»i 



Fig. 5 — Schematic: Composite ringer and composited toll line for toll switchboard 



No. 1 



ringing key to the tip conductor of the cord. This current operates a 

 relay of the line or trunk circuit which applies the proper frequency of 

 ringing current to the line or trunk circuit. By this arrangement one 

 relay in the line circuit accomplishes the same result as was accom- 

 plished by several relays in the composite ringer. As the ringing 

 current leads to the relay in the line are brought through terminals on 

 the frames, the line can be readily changed for any desired frequency 

 of ringing current. 



Elimination of Transfer Key from Face of Inward Switchboard 



In the past the practice has been to provide one or two transfer 

 keys per line for each multiple appearance of the line lamp at the in- 

 ward toll switchboard. The function of these keys is to transfer the 

 inward call from the inward switchboard to the outward delayed 

 positions or to the through positions. With the No. 3 toll switchboard, 

 the use of these transfer keys individual to the line and appearing in 

 the face of each section of the inward switchboard has been discon- 

 tinued and the transfer is effected by a transfer key in the positional 

 circuit which may be used to transfer a call on any line. This key 

 applies 24-volt battery either directly or through a resistance to the 

 ring conductor of the line and operates the proper transfer relay in the 

 toll line and causes lamps individual to that line to light at the out- 



