COLD CATHODE TUBES FOR AUDIO FREQUENCY SICWI- 1381 



If instead of passing a given direct current through a single tube we 

 pass the same current through a parallel combination of n tubes, the 

 resistive component of the combination would be 



R comb. = 



'©' 



n . 



(3) 



= 4..R. 



1/2 



The resistive component of the combination is — - times that of 



single tube passing the same total current. This assumes, of course, that 

 the cathodes of the tubes are covered with glow. Obviously this is not a 

 practical method of attaining a low impedance because of the instability 

 of paralleled individual tubes. It does suggest, however, that by increas- 

 ing the cathode area of a single tube until the glow just covers the full 

 area, a lower impedance is obtained. This has been done experimentally. 



350 



250 



200 



z 



< 150 



100 



50 



10 15 20 25 30 



DC CURRENT IN MILLIAMPERES 



35 



40 



Fig. 7 — Resistive and inductive components of 313-C starter gap impedance 

 as a function of direct current. 



