596 



BELL SYSTEM TECHNICAL JOURNAL 



gotten, however, that thermal tuning is inherently slower in action than 

 electronic tuning, since the latter is capable of frequency correction rates 

 limited, for practical purposes, only by the control circuits, whereas in 



9500 

 Q 



z 

 o 



\^ 9400 



tr 



LU 



0. 9300 



UJ 



U 9200 

 >- 

 o 

 < 



fu 9 100 



-6 -4 -2 



TUNER GRID VOLTAGE 



Fig. 88. — Frequency as a function of the grid voltage for the W.E. 2K45 oscillator" 

 The dashed lines show the variation when the repeller voltage is held fixed for the mid- 

 range value and the solid lines shows the variation with the repeller voltage maintained 

 at its optimum value for each freciuency. These characteristics apply when a 725 ohm 

 biasing resistor is connected in series with the tuner cathode. 



thermal tuning the thermal inertia of the tuning strut limits the tuning speed 

 to rates of the order of 100 mc/sec^ for the 2K45. 



The oj)erating conditions for the 2K45 are given in the table at the 

 bottom of i)age 595. 



