720 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



Fig. 34 — Twin-channel unit. 



plug-in group oscillators, which are also shown in the photograph, to- 

 gether with fuses, alarm lamps, etc. 



Pole mounted repeaters are housed in a cabinet, similar to that used 

 for N. Such a cabinet, equipped with four repeaters is shown on Fig. 37. 



Since a maximum of four repeaters would have to be supphed by one 

 pair of wires, it is not feasible to transmit power for the repeaters over 

 line pairs. Instead the cabinet contains rectifiers and a line voltage 

 regulator for obtaining 130 volts dc from commercial ac supply. For 

 reserve power supply, a cabinet is available containing a 24-volt storage 

 battery and a dynamotor to supply 130 volts dc to two repeaters (or 

 two dynamotors to supply four repeaters) in case of power failure. 



ALARMS 



At terminals a common alarm, operating from carrier failure, performs 

 the functions of: First, dropping all connected subscribers to prevent 



