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BELL SYSTEM TECHNICAL JOURNAL 



wave. That this is actually a minimum was demonstrated experimentally 

 by varying the period of the trigger pulse. Vdc increased for pulse periods 

 both greater than and less than that shown in the diagram. The increase 

 was small and so is of no great practical interest, but it does confirm the pre- 

 diction made on the basis of the above analysis. 



After the tubes have started the switch voltage is nearly double the d-c 

 voltage, and the tubes will operate continuously if the switch voltage is 

 above the minimum operating voltage. The sequence of events near the 

 minimum operating voltage is shown in Fig. 16 (b). During operation the 

 spark delay time is much less than during starting, as indicated by a smaller 

 voltage is estabhshed. 



500 1000 1500 2000 2500 3000 



PULSES PER SECOND 



Fig. 18— Maximum operating voltage of 1B22 tubes in a two-gap circuit as affected by 

 pulse repetition rate for a variety of pulsing conditions as follows: 



Pulse Duration Load in 



Curve in Microseconds Ohms 



1 0.75 55 



2 0.75 30 



3 0.75 15 



4 1.50 30 



Of course, no spark gap tubes are designed to operate very close to their 

 minimum operating voltage. A margin of safety is always maintained. 

 The characteristics of these tubes with a switch voltage at a practical operat- 

 ing voltage is shown in Fig. 1 7 (a) . Gap 1 breaks down between A and A-\- AA 

 and before gap 1 is extinguished gap 2 breaks down between C and C + AC. 

 Since in this case both gaps are conducting simultaneously, the main pulse 

 passes without re-ignition of gap 1. The voltage at the midpoint of the 

 two discharges rises to a value between D and D + AD, due to the rapid 

 change of spark impedance. This sequence always takes place since ample 

 margin is provided. 



