422 



THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



case where superimposed direct current is flowing in the windings, the core 

 structure is formed by a wrap-around assembly of several strips of permal- 



M MM B MS S 



fmSt f^m f^ ' ^x ^^ 



Fig. 3 — Voice, signaling and carrier frequency iia;,.-;v^inicis. 



loy tape and a stack-up of 'T' laminations. One of the signaUng frequency 

 transformers is an adaptation of the type used in hearing aids which was 

 modified to make it suitable for Bell System use. 



