1092 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



plane of its filament with the longitudinal center line of the translator. 

 The combination chimney and guard that is provided as part of the 

 subassembly includes a peep-hole to facilitate filament orientation. 



The lamp, although operated at reduced voltage, generates con- 

 siderable heat. Because of this, its guard and chimney are treated with 

 a cotton flock finish which prevents direct contact with the metallic 

 base and thus the guard may be touched without discomfort. 



The first surface mirrors are mounted so that they are accessible 

 for cleaning. 



COLLIMATING LENSES 



The light level at the photo-transistors may be lessened because of 

 the accumulation of foreign material on the surfaces of the lenses. Be- 

 cause of this, the collimating lenses have been mounted in a frame 

 (see Fig. 37) which makes it convenient to remove them simultaneously 

 for cleaning and to replace them without readjustment. The photo- 

 transistors are red sensitive and, therefore, the focal length had to be 

 determined on this basis. 



CARD CAGE 



The cards are mounted in a cage, as illustrated by Fig. 25. The par- 

 titions are made from magnetic iron. They tend to repel the cards that 

 are mounted adjacent to them when the pull-up and pull-down magnets 

 are energized. This is beneficial when a card close to the partitions is 

 selected, as it gives better assurance of the card dropping reliabily. 

 However, as has been mentioned, it is desirable to mount an uncoded 

 card adjacent to the partitions because the first and last card in a com- 



Fig. 37 — Collimating lenses. 



