334 BELL SYSTEM TECHNICAL JOURNAL 



able period in our Laboratories. Although no magnetron was developed 

 for manufacture from this work, the experience gained was very useful in 

 the concurrent work at 3 cm. where a similar development program of 

 small magnetrons was under way. Specific developments in this category 

 which should be mentioned are: the use of inserts in which the magnetron 

 resonator system is machined, separable from the rest of the magnetron 

 structure; the use of a double lead cathode input seal to reduce over-all 

 thickness; assembly tools for cathode and strap alignment; and the work 

 with small oxide coated cathodes. The work was discontinued here be- 

 cause of extensive commitments for work at 3 cm. and because an active 

 and successful program of development of magnetrons near 1 cm. wave- 

 length was under way at Columbia University. 



The work at the Columbia Radiation Laborator}^ from the start had been 

 concentrated on magnetrons of ver}' short wavelength. The first Columbia 

 magnetron that was reasonably successful was unstrapped, having a vane 

 type resonator system. It was manufactured in small quantities as the 

 3J30. Later, the "rising sun" resonator system was discovered there 

 3J30. Later, the "rising sun" resonator system was discovered as a means 

 of obtaining mode frequency separation. The small scale manufacture was 

 then shifted to the new anode structure, the new magnetron being the 3J3L 

 It was a satisfactory magnetron operating at about 14 kv. and 14 amps., 

 in a magnetic field of 7200 gauss, at a pulling figure of approximately 25 

 mc/s, and a power output of about iS kw. The magnetic field was obtained 

 by an external, separable magnet. The cathode was supported by the 

 conventional radial leads. 



In addition to the work on the "rising sun" structure, work had continued 

 at the Columbia Laborator\- on strapped resonator systems for use at 

 wavelengths near 1 cm. Performance of these magnetrons was quite 

 comparable to that of the "rising sun" variety. 



20.2. The 3 J 21 Magnetron: The Bell Laboratories undertook, in collabo- 

 ration with the Columbia Laboratory, to design a "packaged" version of 

 the 3J31 magnetron for manufacture by the Western Electric Co. At the 

 time, it had not been decided whether the new magnetron should have a 

 strapped or a "rising sun" resonator system. Considerations having 

 primarily to do with manufacturing techniques indicated the latter to be 

 preferable although the former would have been possible. Accordingly, 

 work was started on a "packaged", "rising sun" magnetron to oscillate at 

 1.25 cm. wavelength (24,000 mc/s). It was to have wave guide output like 

 the Columbia model and axial cathode mount dictated by the "packaged" 

 construction. Operating conditions were to be 15 kv., 15 amps., a pulling 

 figure of 25 mc/s, and as much peak power as could be obtained. It was 

 coded the 3J21. 



