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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



gressive size reduction in loading coil cases for exchange area loading which 

 resulted from the coil size reduction, starting with the 602 coil (1925) and 

 including the 612 coil (1927), the 622 coil (1937) and 632 coil (1942). These 

 88-mh loading coils are equivalent to one another in transmission perform- 

 ance. 



Fig. 18 — Progressive case size reduction 1925-1942 200-coil complements — 88 mh. 

 loading coils. Left to right: No. 602 (hard iron-wire core) coils in cast iron case; No. 612 

 (permalloy core) coils in "thick" steel cases, welded joints; No. 622 (molybdenum-per- 

 malloy core) coils in "thick" steel cases; No. 632 (molybdenum-permalloy core) coils in 

 tubular "thin" steel cases. 



22.3 Special Loading Coil for Signal Corps Spiral-Four Cabled'' 



A digression from the main line of the story is appropriate and permis- 

 sible at this jx)int, since the special coils used in loading the very important 

 spiral-four cable carrier systems that were extensively used by the army 

 during World War II were made possible by the development work that 

 led to the standardization of the 632 coils, and by the development of the 

 60-permeability molybdenum-permalloy powder core-material, described in 

 Section 11.1. These 6 mh "army" loading coils used 60-permeability cores 



