AN IMPROVED THREE-CHANNEL CARRIER TELEPHONE SYSTEM 71 



— -^ I -«^ 



-3 



10 20 30 



OUTPUT-DB ABOVE I MW 

 Fig. 17— Gain-load characteristic of amplifier at frequency of 15 kc. 



frequency output, is shown in Fig. 17. Translated into terms of 

 three-channel operation this means a permissible level of 18 db above 

 the transmitting toll switchboard without noticeable distortion or 

 interference between channels due to modulation. 



Power Supply 



The new system is designed to operate at both terminals and 

 repeaters on standard telephone office battery supply of 24 and 130 

 volts. A dry-cell battery is required to supply grid bias to the output 

 tube of each amplifier. A small amount of UO-volt a-c power is also 

 required to drive the Telechron motor in the regulator circuit. The 

 total steady power consumption in a terminal is 88 watts and in a 

 repeater is 56 watts. These figures compare with 220 watts and 164 

 watts, respectively, in the older terminal and repeater. 



Where regulated 24-volt battery is not available, tubes having a 

 slightly greater current consumption are used in combination with 

 ballast lamps. In this case the power used will be somewhat greater. 



Provision has been made for a separate a-c power conversion unit 

 to be used with the system in offices where the usual d-c voltage is 

 not available. This should prove of great value where the provision 

 of a battery reserve is not warranted. 



Signaling 



Standard voice-frequency signaling equipment can be used with the 



new terminals. There is also available a new type of ringer circuit 



in which a single tube functions both as the source of power for an 



outgoing signal and as a detector for an incoming signal. This 



