118 BELL SYSTEM TECHNICAL JOURNAL 



The "A" operator senders are associated with the "A" operator 

 switchboard equipment and are used for the completion of certain 

 classes of calls such as toll and assistance calls. 



A view of the originating marker frame is shown in Fig. 19. There 

 will be a variation in the equipment on this frame for different cities 

 due to the variation in the number of route relays required, the number 

 depending upon the number of central office codes that may be dialed 

 by subscribers and operators. This variable feature is cared for by 

 providing the route relay equipment in bays of 100 codes as shown in 

 the right-hand bay. The terminal fields shown below the route 

 relays on the frame provide the flexible connecting facilities which 

 permit the use of any route relay for any office code and which readily 

 permit changes in routings, variations in trunk group sizes and other 

 features which are subject to change from time to time. 



The power plant equipment provided for the crossbar offices is 

 similar to the equipment now being furnished for all large dial central 

 offices. The principal power supply arrangements provide 48- volt 

 direct current for the operation of practically all the signaling and 

 the telephone transmission circuits. Also several other sources of 

 direct current are provided for miscellaneous purposes as in other 

 standard dial systems. A new distribution scheme for the battery 

 feeders on the frames is employed which reduces the amount of 

 copper required. A common set of 48-volt battery feeders supplies 

 the signaling and talking current for all frames. Individual frame 

 filters are connected across the battery supply leads at the frames 

 where a noise-free battery supply is required for talking circuits. 

 Figure 20 shows a view of the overhead battery cables, conduits for 

 the A.-C. power leads, and the fuse cabinets for the fusing of the 

 battery supply to a row of frames. 



Application 



As mentioned in the first part of this paper, two crossbar dial central 

 offices were cut into service in 1938 and these have now been in com- 

 mercial operation for several months. One of these offices serves a 

 residential area in Brooklyn, while the other serves a congested business 

 area in the midtown Manhattan district of New York City. The 

 operation of these offices under actual service conditions has been 

 highly satisfactory and our expectations in regard to performance have 

 been fully realized. 



This type of system will be used for new offices in large cities instead 

 of the panel system as rapidly as manufacturing and plant conditions 

 permit and the apparatus which was designed for this system will be 

 used in other fields of the telephone system. 



