An Improved Telephone Set 



By A. H. INGLIS and W. L. TUFFNELL 



A new common battery telephone set has been developed and is now in produc- 

 tion which is materially better than previous types in performance and conveni- 

 ence to the user. This paper describes this set, and discusses, as typical of Bell 

 System dleveopment processes, the contributions of the operating, development, 

 and manufacturing organizations to the final design. It also describes the evalua- 

 tion of the design by the controlled service trial, in terms of the results produced 

 in actual service in the hands of the pubUc. 



THE Bell System is now introducing a new and improved common bat- 

 tery telephone set, intended to supplement the present well known 

 combined set first introduced in 1937.^' ^ In view of the established merits of 

 the earlier set, of which something like 25,000,000 are now in the plant, it is 

 of obvious interest to point out the nature and magnitude of the improve- 

 ments represented in the new set which justify the effort and expense of such 

 a change, to discuss some of the factors influencing its introduction at the 

 present time, and to describe the set itseff and its characteristics. 



Before proceeding with this, it is pertinent to define what is meant by an 

 improvement, what sort of changes come under this heading, and what 

 means are available for appraising them. In the Bell System the answers 

 to these questions are looked for in a combination of laboratory and field 

 experience using the effect on service as a major criterion. 



Design for Service 



Improvements may be classified under two general headings. First, there 

 are changes in form and in technical characteristics which improve the 

 quality of the service and increase the satisfaction of the subscriber; the new 

 design may be more acceptable in appearance, easier and more convenient 

 to handle and manipulate, and provide easier and more natural conversa- 

 tion with less effort. Such factors, however, valuable as they are in them- 

 selves, cannot be considered apart from the second important kind of im- 

 provement, which is cost reduction. An improvement, ideally, should offer 

 possibility both of better service and of lower cost. Furthermore a new set 

 may have improved features but, in addition, must offer all the essential 

 service facilities that are currently offered, and work with the existing oper- 

 ating conditions of the plant as it finds them. 



This sort of objective poses important problems of design coordinated 

 with economy which require for a successful solution the knowledge, effort 

 and teamwork such as is provided by the close cooperation developed over 



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