. The Bell System technical journal . he line and throughthe telephone path of the composite set, a 20-cycle current which willoperate the ringing relays of the line or cord circuits. A schematic ofthe composite set and composite ringer, as used with the No. 1 board,is shown in Fig. 5. In general, the composite ringer for the No. 3 switchboard has beengreatly simplified and made a part of the terminating line has been accomplished, as illustrated schematically in Fig. 4, byarranging the line circuit so that a relay may be cross-connected in the 22 BELL SYSTEM TECHNICAL JOURNAL l
. The Bell System technical journal . he line and throughthe telephone path of the composite set, a 20-cycle current which willoperate the ringing relays of the line or cord circuits. A schematic ofthe composite set and composite ringer, as used with the No. 1 board,is shown in Fig. 5. In general, the composite ringer for the No. 3 switchboard has beengreatly simplified and made a part of the terminating line has been accomplished, as illustrated schematically in Fig. 4, byarranging the line circuit so that a relay may be cross-connected in the 22 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 cordsupervisory signal direct without going through the step of changingringing frequencies. Furthermore, the practice of using 20-cycle current in the cordcircuit for linging has been discontinued and ringing is effected in theNo. 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 arelay of the line or trunk circuit which applies the proper frequency ofringing current to the line or trunk circuit. By this arrangement onerelay in the line circuit accomplishes the same result as was accom-plished by several relays in the composite ringer. As the ringingcurrent leads to the relay in the line are brought through terminals onthe frames, the line can be readily changed for any desired frequencyof ringing current. Elimination of Transfer Key from Face of Inward Switchboard In the past the practice has been to provide one or two transferkeys per line for each multiple appearance of the line lamp at the in-ward toll switchboard. The function of these keys is to transfer theinward call from the inward switchboard to the outward delayedpositions or to the through positions. With t
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
