MAGNETRON AS GENERATOR OF CENTIMETER WAVES 315 



Many difficulties were encountered in the early stages of production above 

 those of training personnel to handle small parts and to perform new types 

 of operations. Maintenance of cathode centering through all operations 

 had to be rigidly supervised since off-center cathodes resulted in poor 

 operation. The size and position of the output loop were very sensitive 

 variables directly affecting output power and pulling figure. The latter 

 were also marked functions of variables in the transformer of the output 

 circuit. It was found, for example, that variations in the glass, and particu- 

 larly in the bead supporting the center conductor, were causing considerable 



Fig. 67 — The 730A magnetron (55 kw., 9375 mc/s) — the "straight through" version 

 of the 725A. 



spread in characteristics. Closer tolerance on the glass, involving the use 

 of a molded bead, greatly improved this situation. 



With the very narrow limits specified for the operating frequency of the 

 magnetron, it was essential that the anode pretuning be done very precisely. 

 Here, considerable difficulty was encountered with a pretuning arrange- 

 ment in which the indication of resonance depended on the equivalent line 

 length of the output circuit between the anode block and the detector in the 

 wave guide. Variability in this electrical length caused the actual resonance 

 to vary over a considerably wider range than the required 9375 ± 30 mc/s. 

 By use of a detector connected at the output loop it was possible to reduce 

 the percentage of magnetrons eliminated for being outside the frequency 



