REFLEX OSCILLATORS 



605 



Let us consider the factors involved in scaling from a tube operating at a 

 given frequency to a smaller tube operating at a higher frequency. If the 

 cathode is operated space-charge-limited and the anode voltage is the same 

 as for the larger tube, the total electron current will be the same and each 

 grid wire will intercept as much current and hence receive the same power 

 to dissipate as in the larger tube. Suppose the length of a grid wire in the 

 larger tube is /o and in the smaller tube the length of the corresponding wire 

 is h . Suppose that all the other dimensions of the smaller tube, including 



-12 -10 -8 -6 



TUNER GRID VOLTAGE 



Fig. 96. — Frequency vs tuner grid voltage for the 2K50. 



the diameter of the grid wire, are reduced in the ratio h/U . We do not 

 know a priori whether or not the temperature distribution along the grid 

 wires of the smaller tube will be the same as that for the larger tube; suppose, 

 however, that it is. Then if To is the temperature at some typical point, 

 say, the hottest, on the grid wire of the larger tube, and Ti is the temperature 

 at the similar point on the smaller tube, the power the wire loses by radiation 

 in the large tube, P^o and in the small tube, Pt\ are given by 



Pr^ = Al\T\. 



(13.17) 

 (13.18) 



