1058 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



applications of the switching ampUfier, signaUng facilities are provided so 

 that the switching operation can be controlled remotely. 



An IF distributing amphfier provides three outputs from a single input, 

 all at 75-ohm impedance. It consists of four 404A pentodes, the plate of 

 one tube being connected to the grids of the other three tubes through an 

 interstage network. Individual networks from the three output stages pro- 

 vide the desired distributing branches which are well isolated from each 

 other electrically. 



Switching and distributing amplifiers and a mounting framework are 

 shown in Fig. 14. The two amplifiers have the same physical size and as 

 many as five such units may be mounted in a frame on a plug-in basis. A 

 number of such mounting frames are grouped and mounted on duct type 

 bays to meet the needs of each switching and distributing location. Jack 





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Fig. 14— Switching and distribution amplifiers. 



fields associated with the mounting frames terminate the interbay coaxial 

 trunks through which the switching and distributing connections are made. 

 Various combinations of switching and distributing amplifiers perform a 

 large variety of interconnection functions within the system. Figure 15 

 indicates how these amplifiers may be used to replace a circuit which has 

 failed by a spare circuit. At a transmitting terminal, the regular and spare 

 channels may be paralleled. If a transmission failure occurs in channel 1 

 at one of the auxiliary repeater stations east of the main station, the failure 

 of this channel is noted at the end of the system and service is switched to 

 the spare channel 2. Since channel 1 is good except for the break east of 

 the main station, the remote control for the switching amplifier in channel 

 1 is operated to switch output A of the channel 2 distributing amplifier to 

 channel 1 radio transmitter. Thus channel 1 is connected in parallel with 



