258 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



Fig. 4 — Directional filter unit. High-pass filter 

 with low-pass filter can on rear. 



thought to be great, as all solders used have less tin content than the 

 eutectic alloy. All connecting wires are gold plated instead of the usual 

 tin plating. 



The insulating sub-panels in units are usually made of Perspex, but 

 where the items are subjected to high temperatures (e.g., resistance box), 

 Sintox, a sintered alumina ceramic, or Micalex is used. 



Polytetrafluoroethylene (p.t.f.e.) is another insulant used, and p.t.f.e.- 

 covered wire threaded through copper tube forms the coaxial intercon- 

 necting leads between the can units. 



Careful attention is paid to the mounting of components. Small 

 resistors, etc., are supported by soldering to tags which are the appro- 

 priate distances apart, and multi-limb tags are employed to minimize 

 the number of soldered joints. Where it is essential to solder more than 

 one wire per limb on a tag, they must be soldered at the same time. 



