736 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



assembly and case-wiring arrangements for non-phantom exchange area 

 coils was made during the middle 1920's in solving difficult problems that 

 arose in the design of cases for 200-coil, 300-coil, and larger complements 

 of the new small-size loading coils. The spindle-assemblies of coils were fas- 

 tened to a skeleton frame to which the case pot-cover and the machine- 

 stranded textile-insulated stub cable were attached. The part of the stub 

 cable that extended within the case was subdivided into unit cables which 

 were associated with the individual spindle-assemblies, to which the coil 

 leads were connected, thus eliminating the intermediate spindle cables. After 

 these connections had been made, the complete coil-assembly, with stub 

 cable, was lowered into the coil casing. The case cover was then fastened to 

 the coil casing, and the case filling-compound was poured through a small 

 temporary opening in the cover. 



Assembly and Cabling Changes; Beginning of Use of Loading Units in 

 Individual Shielding Containers: Some of the improved assembly-arrange- 

 ments, above described, were made available for phantom loading units 

 soon after the permalloy-core toll cable coils became available, along with 

 the standardization of the P-B type loading units. Certain differences were 

 necessary, however, in order to permit the assembly of the 3-coil loading 

 units in individual, cylindrical, shielding containers, having one end open. 

 The associated three coils of a unit were mounted on a short hollow dowel, 

 at one end of which was mounted a frame supporting terminal posts for all 

 of the line terminals of the individual coils and the crosstalk adjustment- 

 elements (small inductances and resistances, preselected to meet crosstalk 

 requirements). The cross-connections between the phantom and side cir- 

 cuit coils were made between appropriate terminal posts, and the loading 

 unit main-line terminals were connected to the stub cable conductors at this 

 point, after the crosstalk adjustment-elements were connected in the cir- 

 cuit. The individual loading units in their shielding containers were fastened 

 to a vertical frame by bolts extending through the hollow spindles. This 

 frame was attached to the case cover. The stub cable was a machine- 

 stranded, single piece of paper-insulated cable having the part below the 

 case cover separated into unit cables for the connections to horizontal rows 

 of loading units. 



The loading unit and potting assembly methods are illustrated in Figs. 

 10 and 11 (pages 186 and 188, respectively). Generally similar arrangements 

 were used with the M-type and SM-type loading units. With the standardi- 

 zation of the MF-type loading units, the adoption of cylindrical steel case 

 bodies resulted in some potting assembly changes which are illustrated in 

 Figs. 12, 13, and 14 (pages 192, 193 and 194, respectively). In the medium 

 and large size potting complements, the individual loading units are mounted 



