VACUUM TUBES AS HIGH FREQUENCY OSCILLATORS 109 



for the other tube. At 300 megacycles the higher frequency tube gives 

 an output of 13 watts, while the tube of Fig. 5 no longer oscillates. 

 This difference in behavior is due primarily to the decreases in transit 

 time and in circuit losses, and to the more nearly optimum ratio 

 existing between the inter-electrode capacitances. It is due to a 

 considerably less extent to the increase in the frequency limit set by 

 circuit resonance. 



A Still Further Departure in Construction 

 The tube illustrated in Fig. 10 represents a still further departure 

 from conventional construction with a corresponding increase in the 



Fig. 10 — This tube will oscillate at frequencies up to 740 megac\cles. Note the 

 absence of the usual press and the extremely small size of the elements. 



frequency limit. Fay and Samuel report an output of 6 watts per 

 tube at 500 megacycles and a frequenc^^ limit of 740 megacycles. 

 Unusual features of the design are: The complete elimination of the 

 usual press, the close spacing of the leads and the special construction 

 of the tube elements, particularly the grid, made necessary by their 

 small size. The grid is in the form of a number of straight wires 

 (parallel and equidistant from the axial filament) supported by cooling 

 collars at each end. The plate, in spite of its small size, can dissipate 

 40 watts with safety. 



