304 



BELL SYSTEM TECHNICAL JOURNAL 



resonator system, straps, cathode, and output circuit. In Table II are 

 given dimensions and other data concerning these magnetrons. 



The resonator system has eight hole and slot type cavities. Its anode 

 length is 4 cm., double that of the 706AY-GY. It is strapped with double 

 ring shielded straps of special design which could be stamped out of sheet 

 copper and oven brazed in position in a wide ledge trepanned around the 

 interaction space into the ends of the anode block. These straps were 

 easier to control in dimensions than the echelon straps, used in early experi- 

 m.ental models, which had made necessarj^ the development of a pretuning 



Fig. 63 — A view of a cut-away 720A-E magnetron (1000 kw., -^2800 mc/s) showing the 

 large cathode end disks and the impedance transformer sections in the output circuit. 



technique. The large number of wire straps used had made it impossible 

 to predict from visual inspection that a given anode would eventually oscil- 

 late at a specified wavelength. The straps were adjusted manually to bring 

 the frequency of resonance determined before sealing and pumping into the 

 required range. These heavily strapped models operated at efficiencies up 

 to 65 per cent, but their initial operating wavelengths were near 13 cm. 

 The high operating efficiency was achieved at the required wavelength by 

 scaling the structure. The increase in magnetic field required by the scaling 

 was achieved without increase in magnet size by incorporation of steel disks 

 in the end covers of the magnetron. The new stamped straps required 

 considerably less manipulation during pretuning than the echelon straps. 



