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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 195G 



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Fig. 7 — Plug-in units. Left to right, reading amplifier, match unit varistor 

 cluster, individual varistor, match and-gate, transistor, and pulse stretcher. 



In wiring the rack, use of individually-shielded conductors was held 

 to a minimum. The cable between the drum unit and the reading ampli- 

 fiers was composed of standard switchboard wire, shielded as a unit by 

 removable sheet-metal enclosures, thus greatly reducing the bulk as com- 

 pared to the usual bundle of coaxial cables. 



The remainder of the wiring, which carries relatively high-level signals 

 from unit to unit within the frame was also in the form of cables of switch- 

 board wire; this type of wiring was tried as an experiment for micro- 

 second pulse work, and was found to be successful in this instance. 



Under normal conditions the entire translator, with the exception of 

 the tube filaments and drum drive motor, operates from the standard 

 plant batteries of +130 and —48 volts. Commercial 60-cycle power is 

 normally used for filaments and motor; the motor is duplex and is de- 

 signed to transfer automatically to the 48-volt plant battery in case of' 

 power failure, and the same provision would have to be made for the 

 filaments in the event of a telephone plant installation. i 



Magnetic Drum Unit \ 



The magnetic drum unit is located at the bottom of the rack, as shown i 

 in Fig. 1; a close-up view with one of the covers removed is shown in 

 Fig. 8. A mounting casting supports the machine directly on the floor, 

 straddling the lower member of the rack so that no load is imposed on 

 the rack structure. The drum rotates about a vertical axis and is housed 

 in two cast-iron end-bells spaced by a cast-iron shell. The end-bells carryi^ 

 the bearings for the drum, and serve to mount the motor, while the shell- 1 

 casting rigidly locates the magnetic heads, each very close to the drum 

 surface. This design requires a minimum of floor space, insures accurate 

 bearing alignment, provides a convenient location for the magnetic 

 heads, and permits the use of tightly-fitting gasketed covers to exclude 



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