1386 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



0.2 



0.4 0.6 0.8 1 2 4 6 8 10 



FREQUENCY IN CYCLES PER SECOND 



20 30 

 X103 



Fig. 13 — Resistive component of impedance as a function of frequency for 

 different neon filling pressures. Cathode gap = 0.024 in. 



Fig. 14 shows the variation of the resistive component of tube im- 

 pedance as a function of frequency for several cathode gaps and at a 

 fixed density of filhng gas. For both Figs. 13 and 14, the current was 

 adjusted for optimum negative resistance. 



It can be seen from Fig. 13 that the choice of a neon filHng gas at a 

 pressure near 60 mm and from Fig. 14 that a cathode gap near 0.024 inch 

 could be expected to yield a negative resistive component of impedance 

 which is reasonably insensitive to filling pressure and which is also 

 constant in value over the voice frequency range. This justifies the choice 

 of cathode gap and filling pressure used in the tube on which the data 

 of Figs. 11 and 12 were taken. 



One other parameter of interest is the limit of anode-to-cathode dis- 

 tance. This too is a function of cathode gap and gas density. A typical 

 curve taken for the same cathode geometry and gas filling as used for 

 Figs. 11 and 12 is shown in Fig. 15. It is seen that the negative resistive 

 component is essentially independent of anode distance for a distance 

 of approximately 0.050 inch. This means that the breakdown voltage of 



