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BELL SYSTEM TECHNICAL JOURNAL 



dimensions of the 700A-D magnetrons to obtain the frequency range de- 

 sired. The cathode structure was improved, making use of later develop- 

 ments. Its diameter was changed from 0.8 cm. to 1.0 cm. in order to increase 

 the maximum current to which operation in the ir mode is possible. The 

 anode diameter was retained; the operating conditions were not appreciably 

 affected. It was necessary to retain the original form of output circuit. 



Fig. 53 — The4J42 tunable magnetron (40 kw., 660 to 730 mc/s) — the tunable replacement 

 for the 700A-D magnetrons. The worm drive in the mounting bracket operates the 

 tuning mechanism enclosed in the end cover of the magnetron. Note the improved input 

 leads and protective housing (see Fig. 46). 



In Fig. 53 is shown an external view of the 4J42. In Table I are given 

 operational data and other characteristics. The performance of the 4J42 

 is as good or better than that of the corresponding magnetron in the 700A-D 

 series. 



14.3 The 4J51 Magnetron: The 728A-J series of fixed frequency mag- 

 netrons was replaced by the 4J51, covering the frequency band of 900 to 

 970 mc/s. An external view of the magnetron is shown in Fig. 54, As in 

 the 4J42, the resonator system is a modification of that used in the fixed 

 frequency prototype, strapped on the untuned end by double ring strapping. 

 Satisfactory mode frequency separation is maintained by increasing the 



