1080 THE HELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



controlled l)y the configuration of the gahi-adjusting network, consist- 

 ing of se\'eral inductors, capacitors, and resistors. These components 

 may be arranged in a variety of ways to obtain the gain and frefiuency 

 shaping characteristics desired for each type of line facility. 



The E3 repeater employs a Western Electric 407A twin-triode elec- 

 tron tube of the 9-pin miniature type. The circuit is arranged so that the 

 current for the heater of the tube can be obtained from 24- or 48-volt 

 office battery. The heater poAver is 2 watts and the plate current is 

 nominally 5 milliamperes. 



Equipment 



The objective of the equipment design of the E2 andE3 repeaters w^as 

 to produce a repeater that would be simpler to manufacture, easier to 

 engineer, install, and maintain, and make more efficient use of the 

 mounting space, particular^ on 23-inch bays, than the present El 

 repeater. Because of the large demand, savings in manufacturing costs 

 were realized by using a compact aluminum die-cast shell to house the 

 repeater components. To facilitate manufacture, parallel thermoplastic 

 strips were used for the mounting of "pigtail" type of components.^ 

 Further savings in shop costs were obtained by coordinating the designs 

 of the E2 and E3 repeaters for maximum interchangeability of parts. 



Engineering and installation effort has been reduced considerably by 

 avoiding engineered options and by arranging the equipment so that 

 the maximum portion of the assembly and wiring work is performed in 

 the shop. Testing and maintenance routines are simplified by arranging 

 the repeaters as plug-in units that can be removed from their bay posi- 

 tions and plugged into a portable test set located in a more convenient 

 working space. In this w^ay, the network strapping and any repair work 

 which may be required on a repeater need not be performed while the 

 repeater is in place, or is in a congested area. Maintenance and service 

 interruptions are reduced to a minimum length of time by replacing a 

 defective plug-in unit with a spare for immediate restoration of service, 

 and the faulty repeater repaired at a more convenient time. 



REPEATER UNITS 



Both E2 and E3 repeater units use the same rectangular die-cast 

 chassis, shown in Fig. 19. The front section of each unit carries the elec- 

 tron tube and test pin jacks which must be accessible for testing and 

 routine maintenance. The gain-adjusting network strapping terminals 

 are arranged, in three rows, along the left side of the repeater, and are 

 accessible only after the unit is removed from its mounting shelf. 



