MAGNETRON AS GENERATOR OF CENTIMETER WAVES 319 



A photograph of the 2J55 magnetron is shown in Fig. 69 and operating 

 data are included in Table III. 



18. Tunable Magnetrons for Wavelengths near 3 Centimeters 



18.1 Tlie 2J5I Magnetron: As in the 20 to 45 cm. wavelength region, 

 the demand arose for tunable magnetron replacements when fixed frequency 

 magnetrons had become available in the 3 cm. band. A significant step 

 toward satisfying this demand was taken at the NDRC Radiation Labora- 



Fig. 70 — An external view of the 2J51, tunable, "packaged" magnetron (55 k\v., 8500 



to9600mc/s). 



tory at Columbia University in 1943 when a tuned, "packaged" magnetron 

 was built around a 725A anode structure and output circuit. The tuning 

 scheme used was that of variation of resonator inductance, as discussed in 

 PART I, by a so-called tuning head consisting of a set of pins which project 

 into the holes of the resonator system. The mechanism for driving the 

 tuning head is contained inside one of the magnet pole pieces. The other 

 pole piece carries the axial cathode mount. Two magnets are clamped to 

 opposite sides of the pole pieces in the usual "packaged" construction. 

 These and other details are shown in the photographs in Fig. 70 and 71 of 

 complete and cutaway models of the magnetron, coded the 2J51, as it was 

 put into production at the Western Electric Co. 



