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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1956 



amplifier and some of the connected apparatus, is shown in Fig. 12. The j 

 uppermost channel on this diagram is typical of all five channels. Re- 

 sistors Ri to R5 are proportioned so that the potential at point c assumes 

 a value of +115 volts for either of the two acceptable conditions 

 of match: (1) code-relay unoperated and reading amplifier not drawing 

 plate current, or (2) code relay operated and reading amplifier drawing a 

 pulse of plate current. Whenever either of the two possible conditions of 

 mismatch exists, the potential at point c assumes a value about 15 volts 

 higher or lower, depending on the nature of the mismatch. Resistor r6 

 is introduced for protective purposes only. Varistor vri limits the nega- 



+130V! 



CODE-CHECK 

 RELAYS 



Fig. 12 — Match unit and differential amplifier circuit. 





