CARD TRANSLATOR FOR NATIONWIDE DIALING 



1051 



The phototransistor is coupled to the amplifying transistor by trans- 

 former Tl. This permits convenient matching of impedances and separa- 

 tion of the dc bias voltage. A voltage limiting varistor, V, is connected 

 across the input of the transformer to limit surges which might other- 

 wise damage the amplifying transistor. The circuit of the transistor 

 amplifier is a conventional arrangement. 



Voltage gain of the amplifier, including the input transformer to the 

 gas tube, varies from 40 to 100. However, when operating in the trans- 

 lator, the phototransistors normally will drive the amplifier to saturation 



TRANSISTOR AMPLIFIER 



MODULATED] T 



LIGHT 



sion. 



PHOTO 

 TRANSISTOR 



I 



I 



+ 130V 6 R 



T -24V 



^ J^||^ 



ASSOCIATED 

 EQUIPMENT 



*1 



+ 130V 



Fig. 8 — Electrical section of channel circuit. 



which limits the output to 160 volts positive peak. For the purpose of 

 guaranteeing operation, a minimum output voltage of 38.5 has been 

 set as a rejection point for a phototransistor-amplifier combination. 



The output of the transistor amplifier is normally sufficient to break 

 down the control gap of the cold cathode gas tube. Sufficient current 

 flow^s in this control gap to insure reliable transfer to the main gap when 

 the output control relay O in the associated equipment operates. To 

 aid deionization of the gas tubes, the bias of —24 volts is removed from 

 the control anode just before channel operation is required. The relay R, 

 which replaces the bias voltage with ground, is operated by a circuit 

 which checks that the card being dropped is completely down. This 

 "down" check circuit utilizes the two index holes in the card which are 

 never enlarged and employs two phototransistors to detect the presence 

 or absence of light through these holes. 



Fig. 9 shows the card down check circuit. It differs from the routing 

 information channel circuits in that the operation of a relay is required 



