MAGNETIC DRUM TRANSLATOR FOR TOLL SWITCHING OFFICES 733 



sioned by reading a "1", will be a negative-going pulse of approximately 

 40-volt amplitude from a standing potential equal to the plate supply, 

 + 130 volts. As a precaution against false signals, an externally-mounted 

 plate-feed resistor is provided to establish at the output a condition cor- 

 responding to that of no signal present when the amplifier is removed 

 from its receptacle. 



Timing Unit 



The timing unit accepts an approximately sinusoidal timing-wave sig- 

 nal from the upper timing head, and converts this signal into two pulse- 

 trains, each having 1,024 narrow pulses per drum revolution, designated 

 as A sync and b sync, alternating in time and available on separate out- 

 puts for controlling all the rest of the circuit action of the translator. A 

 block-schematic indicating how the pulse trains are produced is shown 

 in Fig. 1 1 . 



The general procedure for converting from a sine-wave to a synchro- 

 nous train of short pulses, two per cycle of input, may be traced through 

 the upper channel of the drawing. The signal, as represented by voltage 

 trace 1, is amplified and clipped until a steep-sided square wave is ob- 

 tained; this wave, trace 2, is applied to a push-pull phase inverter from 

 which a pair of oppositely-phased outputs is obtained. Each of the two 

 outputs is then differentiated by means of an r-c network, and the nega- 



+ 130V 



^pvw 



INPUT 

 FROM HEAD 



OUTPUT 



A A A -' ^S"^ 



Fig. 10 — Reading am])lirior circuit. 



