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BELL SYSTEM TECHNICAL JOURNAL 



limits at final test from more than 50 per cent to less than 1 per cent. At 

 one point in the development, when it appeared that the frequency spread 

 could not easily be reduced, a tuning screw mechanism was designed with 

 which the frequency of the resonator system could be varied by movement 



8 10 12 14 



DC CURRENT, I, IN AMPERES 



Fig. 68— A typical performance chart of the 725A and 7,iOA magnetrons (9375 mc/s). 



of a plug through the side wall of one resonator and which could be adjusted 

 from outside the vacuum envelope at the final acceptance test. Although 

 tlie mechanism was built, tested, and found to operate satisfactorily, the 

 improvement of the pretuning technique made its adoption unnecessary. 

 During the initial stages of production it was verified that the pulling 

 figure of the 725A and 730A could be adjusted within limits by variation of 

 the position of the end plate shorting the wave guide section into which the 



