Instruments for the New Telephone Sets * 



By W. C. JONES 



Transmitters and receivers for use at subscribers' telephone 

 stations have been designed which not only materially improve 

 transmission but also simplify manufacture and facilitate main- 

 tenance. This paper discusses these improvements and describes 

 some of the new design technique employed in their development. 



AS a result of continuous development work on transmitters and 

 receivers for use at subscribers' telephone stations, new instru- 

 ments have been designed which not only materially improve trans- 

 mission but also embody features which simplify manufacture and 

 facilitate maintenance. These instruments are now being produced 

 for use in handsets, desk stands and wall sets in the Bell System.^ 



In many respects these instruments represent outstanding advances 

 in transmission instrument design and performance. It is the purpose 

 of this paper to discuss these improvements and to describe some of the 

 new design technique employed in their development. The data pre- 

 sented will be confined almost entirely to physical measurements which 

 serve to define the performance characteristics of the instruments. 

 The interpretation of these data in terms of their relationship to the 

 characteristics of associated apparatus and their overall reaction on 

 transmission in the telephone plant is covered by a companion paper 

 dealing with the transmission features of the new sets.^ 



Handset Applications 

 The new transmitter unit with an adapter was first introduced in 

 1934 as a replacement for the earlier type of handset transmitter.^ 

 There are now about five million of these transmitters in use in the 

 plant of the Bell System. While experience has shown that they effect 

 an outstanding improvement in performance they do not take full 

 advantage of the possibilities of the unit type of construction from the 

 standpoint of simplification, owing to the fact that a number of 

 additional parts are required to mount the unit on the existing type 

 of handset handle. The advantages of the unit type of instrument 

 have been realized in a new design of handset introduced during 1937, 

 about a million of which have been produced. This handset is shown 



* Presented at A.I.E.E. Summer Convention, Washington, D. C, June 21, 1938. 



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