MAGNETIC DRUM TRANSLATOR FOR TOLL SWITCHING OFFICES 735 



tive-goiug spikes, traces 3 and 4, are combined in a negative-going or 

 gate of crystal diodes. 



These spikes, trace 5, are used to trigger a cathode-coupled single-shot 

 multivibrator, designed to give a rectangular pulse of about one micro- 

 second duration. The multivibrator drives a pair of identical out- 

 put stages: one furnishes the recjuired a sync pulses to other equipment 

 in the translator bay, and the other delivers its output to a coaxial con- 

 nector so that, when required, the pulses may be furnished to the admin- 

 istration unit. 

 I The B sync pulse-train is produced in the lower channel shown in Fig. 

 11. After some linear amplification, a part of the original input sine-wave is 

 applied to a vacuum tube integrator circuit. The constants of the inte- 

 grator are such that it provides very nearly a quarter-period of phase 

 shift even if the drum varies from its nominal speed. The output of the 

 integrator is then treated in the same manner as that described for the 

 direct input, with the result that the required b sync pulses are produced. 



The timing unit also contains a third channel which accepts the once- 

 per-revolution signal from the special head adjacent to the single-tooth 

 wheel. The output of this channel provides the fiducial signal, on a low- 

 impedance basis, for administrative operations. 



The Translation Selecting Unit 



This unit, which appears as the bottom panel in the photograph. Fig. 6, 

 performs a number of successive steps in making its selection. These are: 

 (1) recognition of a match between input information from a decoder 

 .seeking a translation, and the unique corresponding information from 

 .the drum, selected from the flow of continuously-presented information; 

 '(2) production of a gate-opening pulse whose leading edge is substanti- 

 ally coincident in time with the leading edge of the particular a sync 

 1 pulse corresponding to the entry for which the match occurred; (3) acti- 

 \ation of a slot-spanning pulse circuit to bridge the time interval until 

 jthe next-following b slot; (4) production, at a separate output, of another 

 igate-opening pulse whose leading edge is substantially coincident in time 

 with the leading edge of the identified b sync pulse. These actions will 

 now be considered individually. 



(1) Recognition of Match 



Responsibility for this function is divided among a group of eight 

 match-units operating with their associated differential amplifiers. Each 

 match-unit is capable of comparing the inputs from five code-relays with 

 the potentially-matching outputs of five reading amplifiers. 



A circuit schematic of one of the units, with its associated differential 



