THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



location or orientation of parts, the cast resin frameworks are milled or 

 spot-faced. The structure used in the input interstage, shown in Fig. 5, 

 is an example. Circuit elements are wired to pins driven into the casting 

 or, in some cases, to wires imbedded in the material. All wiring can 

 thus be made direct with a minimum of bending and no doubling back, 

 resulting in a reproducible and uniform product. 



The entire amplifier is housed in a sealed die cast container to protect 

 the components from humidity damage. Dessicant is enclosed in each 

 amplifier. It would have been desirable to make this housing of alumi- 

 num, but the high melting point of this metal makes it impractical for 

 such a large casting to meet the air-tightness requirement. A zinc-base 

 die casting alloy was therefore used. Sealing is accomplished by rubber 

 gaskets at all openings for connections and at the joint between the two 

 parts of the housing. The removable part of the casting which serves 

 as a cover is made as large a part of the total housing as possible, in 

 order to provide maximum accessibility for maintenance of the units 

 mounted on the base. The entire housed unit is arranged to mount on a 

 relay rack mounted panel by means of slides which are self-locking. 

 Signal and power connections are made by means of flexible cords which 



Fig. 4 — Line amplifier, wiring side. 



