REFLEX OSCILLATORS 603 



and AX = X„ - Xo = W^ iT„ - To) (13.13) 



or X - Xo = (X„ - Xo)(l - e-^'""^). (13.14) 



Thus the behavior of this type of tuner may be described by a time constant 



which is given by r = - . This has been verified experimentally for the 

 k 



2K50, in which this constant has been found to have a typical value of 1.3 

 seconds. 



The instantaneous tuning rates at a given wavelength based on full on- 

 full oflf operation can be shown to be 



f = --^(/-/J heating (13.15) 



at T Jm 



f = -7(/o-/) cooling (13.16) 



at Tjo 



where /o is the frequency at zero tuner power 



/„ is the frequency at maximum permitted drive. 

 Figure 94 shows the instantaneous tuning rate as a function of frequency 

 on heating and cooling. 



Typical power output versus frequency characteristics for the 2K50 are 

 shown in Fig. 95. Curve A shows the power output with the repeller voltage 

 optimized at each frequency while Curve B gives the variation when the 

 repeller voltage is set for an optimum at the center of the band and_^held 

 fixed as the frequency changes. For constructional reasons the spacing 

 between the repeller and second cavity grid is fixed in the 2K50 so that on 

 a proportional frequency basis the range between half power points with 

 fixed repeller voltage is smaller for the 2K50 than for the 2K45. 



Figure 96 shows the frequency vs. grid voltage characteristics for the 

 2K50. For normal operation with full on-full ofif operation the grid voltage 

 is switched between zero and cutoff. 



H. A Millimeter Range Oscillator 



During the latter stages of work on the 2K50 development, work was 

 started on an oscillator for a wavelength range around .625 cm. The design 

 of this developmental tube known as the 1464XQ was undertaken. 



There are several difficulties in going from 1.25 cm. to .625 cm. Greater 

 accuracy of construction is required and the cathode must be operated at a 

 higher current density. The greatest difficulty arises from the fact that 

 the grids cannot be directly scaled in size from those used in tubes for longer 

 wavelengths. 



