90 BELL SYSTEM TECHNICAL JOURNAL 



not ionize in a cavity of restricted tuning range. Every tube must resonate 

 within the range of the tuning adjustment, and the transmission loss through 

 the test cavity must not be excessive. 



Two additional tests are made at the time the d-c igniter characteristics 

 are checked. One, igniter interaction, is important in the 721 A, the 10 

 cm. TR tube. This tube has rather large openings in its cone tips, so that 

 if the igniter electrode is sealed in too close to the cone tip, the glow discharge 

 which surrounds it may extend out into the gap. Such a defective tube will 

 show igniter interaction; the low-level loss through it will be more when the 

 igniter arc is on than when it is off. Normal tubes do not show this effect. 



The 724B 3 cm. TR tube has such a tiny opening in its cone tip that 

 igniter interaction does not occur. The tube is more subject to igniter os- 

 cillations, perhaps because it is filled to a higher gas pressure. The conse- 

 quences of these oscillations was explained in the section on The Spike. 

 Igniter oscillations are usually due to an improper gas filling, and are de- 

 tected by means of a cathode ray oscilloscope. 



The above tests are made on each tube as it comes off the production line. 

 Some additional tests are made on selected samples to insure that the quaUty 

 is being maintained. Selected tubes are subjected to mechanical shock 

 tests and to temperature variation tests to verify both their resistance to 

 thermal changes and that their temperature coefficient of frequency is not 

 excessive. Absolute recovery time, Q, and leakage power tests are made 

 on these tubes, and some are set aside for life testing. By all these tests 

 the important electrical properties of the tube are under constant scrutiny 

 and the danger of shipping defective tubes is minimized. The importance 

 of adequate testing can hardly be over-emphasized, as a defective TR tube 

 may render a whole radar system inoperative. 



Acknowledgements 



Because of the very close liaison maintained during the war period between 

 various industrial and governmental laboratories, the developments de- 

 scribed in this paper were carried on with the constant advice and criticism 

 of many individuals. It is not therefore possible to assign credit to specific 

 individuals for any particular aspect of the work with any certainty. The 

 authors would be remiss, however, were they not to call attention to the 

 many contributions made at the M.I.T. Radiation Laboratory particularly 

 by members of the group under the direction of Dr. J. R. Zacharias and later 

 Dr. A. G. Hill. Colonel J. W. McRae assisted in the early formulation of 

 the TR problem and Captain A. Eugene .Anderson did much of the original 

 development work on the 724B tube while at the Bell Laboratories and was 

 later involved in the formulation of test methods and test hmits in connec- 

 tion with his Signal Corps work. Mr. C. F. Crandell of the Southwestern 



