1328 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954: 



in Fig. 12, the middle diagram of which represents the voltage on the 

 grid of the dc amplifier b. The voltage on the grid of this amplifier mil 

 thereafter build up slowly as shown at (b) because of the ot (operate 

 time) resistor and C3 capacitor. In this illustration it is assumed that the 

 incoming dial pulse has a duration of only 40 milliseconds, which is 

 shorter than desired. In this particular case the rf relay operates about 

 at time (b) and the r relay at point (c), which is just prior to the end of 

 the pulses. It is therefore necessary, in order to obtain a corrected output 

 signal, to delay the release of the r relay. This is accomplished by causing 

 current to flow into the grid of the dc amplifier tube b from time (c) to 

 time (d). This current comes from energy stored in C2 from battery d 

 prior to time (c) and from the positive transient at the plate of tube a 

 generated by the end of the pulse. At time (d) the rf relay releases, and 

 the voltage on the grid of the dc amplifier b decays along the line from 

 (d) to (e), at which point relay R releases. The result is that the r relay 

 has sent on a pulse that has been corrected from an original 40 to a final 

 50 milliseconds. It is possible but uneconomical to build a unit that 

 would achieve perfect pulse correction to 60 milliseconds, but when a 

 number of toll lines are in tandem, the pulses wdll have to pass through 



75MS 25MS 



SERIES OF 

 INCOMING DIAL 



PULSES OF 



2600 % TONE 



(TOO LONG) 



GRID VOLTAGE 



ON DC 

 AMPLIFIER (B) 

 IN FIGURE 11 



OUTPUT CURRENT 

 IN CIRCUIT E 

 OF FIGURE 11 



CORRESPONDS TO 

 75 MS INTERVAL 



Fig. 13 — Wave forms for shortening of long dial pulses. 



