AN IMPROVED TELEPHONE SET 269 



prior to installation. Company records of station plant maintenance effort 

 for both types of set were marked for easy subsequent review and the sets 

 individually numbered. On any service troubles requiring removal, the set 

 was returned to the Laboratories for examination. 



The phases of the trial relating to the relative maintenance effort re- 

 quired for the two types of set were expected to last for several years. This 

 trial was not expected to show any marked difference for the first year or 

 two of service unless there should be major defects not uncovered in the 

 initial trial. Thus far there has been no indication of any such factor. One 

 very definite reduction in maintenance effort has been the essential elimi- 

 nation of station visits to adjust ringer volume. 



The trials have indicated that dialing and ringing performance in service 

 are at least equivalent to present design with respect to circuit holding time, 

 although dialing over a much wider range of positions is possible and the sub- 

 scriber has been given control over his ringer volume. 



The trials have also provided confirmation of the potential value of the 

 better transmission, dialing, and ringing capabihties of the new set. These 

 gains can be used either for extension of range of operations from the central 

 office or in increased use of finer gauge cable conductors. Other advantages 

 are provided including the fact that the new set can be used at most stations 

 where present practice calls for local battery talking sets. Equalization, to- 

 gether with the better dimensional fit of the handset, particularly for women, 

 decreases the range of transmitted levels. This is brought about by a decrease 

 in the proportion of low levels without affecting the high. 



Acknowledgements 



The development of the 500-set offers a good example of Bell System inte- 

 gration of development, manufacturing and operating experience in the pro- 

 duction of apparatus which is of value both to the telephone company and 

 to the public in providing the best telephone service in the most economical 

 manner. The process of development will continue while the 500-set is in 

 production and improvements in the direction of lower costs or of better per- 

 formance, as they become available, will be incorporated. As this work con- 

 tinues, the primary responsibility for maintaining the intent of the design 

 uniformly in the product is in the hands of the Western Electric Company. 

 The Bell Telephone Laboratories cooperates with the Western Electric Co. 

 in this work and prepares reports for the use of the operating organizations 

 of the system on the quality of the product. 



A roster of individual contributors to the development of the new set is 

 too long to be included here. This also applies to the names of those to whom 

 the authors are so greatly indebted for assistance in the preparation of this 

 paper. 



