596 BELL SYSTEM TECHNICAL JOURNAL 



non-uniform anode build-up and a shortened life. Furthermore, in order 

 to prevent failure of the tube, due to sputtered material destroying the 

 insulation of the interior glass walls, the inside diameter of the cathode was 

 enlarged near the open end, thus confining the sparking to the deeper por- 

 tion of the cathode cylinder. 



As discussed in II- (d) the starting voltage of a pair of fixed gap tubes is 

 particularly important. The operating voltage of the tubes in this case is 

 approximately 4 kilovolts which is derived from the resonant charging of the 

 pulse shaping network condensers from a high voltage supply of about 2.2 

 kilovolts. The open circuit voltage of this supply is about 2.7 kilovolts. 

 This, then, is the voltage available for starting the gaps. In order to make 

 the gaps start at a voltage well below this value, corona points were intro- 

 duced at the end of the cathode opposite the end of the anode, a small 

 quantity of radium was also introduced in this region, and the anode diame- 

 ter was reduced to the lowest value consistent with long life. The effective- 

 ness of the corona points and the radium was reduced by the sputtered 

 material during the life of the tube, but the irregular deposition of this 

 sputtered material favored the production of corona and actually reduced 

 the starting voltage to a lower value than that for a new tube. 



The tube was designed for fuse clip mounting but it was found that the 

 acceleration imparted to the tube when it was snapped into heavy clips was 

 greater than that encountered in flying service. Accordingly, a special 

 mounting was devised so that the tube would not be broken when being 

 installed in the radar set. By the end of the war these tubes had been 

 installed in approximately 15,000 radar equipments. 



W.E. 1B29 



The 1B29 fixed gap tube is similar in constructional details to the 1B22 

 except that it is smaller, the gap spacing being only 90 mils. An exterior 

 and a cross-sectional view of the tube are shown in Fig. 22. 



The gaps were designed to switch 2.8 kilovolts and to pass a peak current 

 of about 27 amperes for 0.75 microseconds at a repetition rate of 2000 pulses 

 per second. The main design problems were those of adequate life and sta- 

 bility of tube drop during conduction. 



The small size of these gaps resulted in a life of only 300 hours which was, 

 however, quite adequate for this application. As pointed out in IT(b) the 

 argon was added to the hydrogen to ensure a uniform low impedance on 

 sparking. The extremely small peak current required an increase in the 

 amount of argon to 50% instead of the usual 25%. 



In mechanical construction, the 1B29 is essentially a scaled-down 1B22. 

 Because of the smaller size of the tube, no new problems existed in making it 

 rugged. 



