VACUUM TUBES FOR RADAR I. F. AMPLIFIERS 



405 



5.3 Fixed Tuning 



It is highly desirable to design the IF amplifier with lixed tuning in order 

 to minimize the number of adjustments that need to be made when tubes 



UJ UJ 



a. Q- 



D < 



UJ _j 



Q-Z 



screen-grid: 120 V 



Eci = -1 



D UJ 

 O Q. 



z 



d 2 



5 



40 80 120 160 200 240 -7 -6 -5 -4 -3 -2 -I 



PLATE POTENTIAL IN VOLTS CONTROL-GRID POTENTIAL IN VOLTS 



HEATER VOLTAGE 

 = 6.3 VOLTS 



Z = 



-7 -6 -5 -4 -3 -2 -I 

 CONTROL-GRID POTENTIAL IN VOLTS 



Fig. 14 — Average 6AK5jcharacteristics. 



are changed. The difficulty immediately arises that, since the tube capaci- 

 tances are usually a large fraction of the total shunt capacitance of each 

 coupling network, the variations in capacitance from one tube to another 

 become very important. It is essential that, after the amplifier is lined up 

 at the factory with standard tubes, any stock tubes taken at random shall 

 give satisfactory performance in the amplifier. This requires close control 



