ADMITTANCES OF J'ARALLEL-FLANE ELECTRON TUBES 641 



Solving (20) for ^17^2 and remembering that V1/V2 = rn , 



Tf = 721 A/ — 



V2 y nii 



(21) 



If (19) and (21) are substituted in (18), one finds 



721 y mx\_ o6m2 ji^J 

 By using (14) and (16), y-n can then be written as 



1 



' / — r 



^ J22 , /mi . I 

 721 ~ — 4/ — 1 + .^ 



721 \ Vll L 66W..>'22 



1 



_ 1 — ynRs 



(23) 



Several 1553 triodes were available for study. Typical experimental 

 results obtained with two of them are shown in Figs. 20, 21, and 22. The 

 triode used in obtaining the data of Fig. 20 had input and output .spacings of 

 0.65 and 12 mils, respectively. The cathode and anode diameters were 180 

 mils. The grid opening was 250 mils and was wound with 0.3 mil tungsten 

 wire at 1000 strands per inch. In the figures, Vg and Vp represent the d-c. 

 grid and plate potentials, respectively. 



There are a number of interesting things to observe in Fig. 20. As with the 

 diode, 611 for a large negative bias approaches the "cold" value computed 

 from the capacitance. However, as anode current is drawn, bn drops rapidly 

 to a much lower value than was the case for the diodes. The conductance ^u 

 behaves somewhat like g for the diode. 622 is equal to the value computed 

 from the grid-anode capacitance and is not appreciably influenced by the 

 electron stream. ^22 was very low with a magnitude of slightly less than 1000 

 micromhos at maximum anode current. It is not shown in the figure. The 

 transadmittance ^21 is worth considering. When the bias is several volts 

 negative, y2i has a value of about 9000 micromhos. This is about 50 times as 

 high as one would expect from a consideration of the electrostatic capacitance 

 between the cathode and anode of the tube. This effect has been investigated 

 more fully and is discussed in another paper.-^ As the tube starts to draw 

 plate current, ^21 rises and reaches a maximum of about 40,000 micromhos. 

 The low-frequency transconductance was measured and is plotted in the 

 figure. It will be observed that the high-frequency transadmittance is only 

 slightly lower than gm . This is in agreement with the theories of Llewellyn. 

 The agreement appears reasonable when one remembers that, in the theo- 

 retical analysis, the magnitude of the ratio yn/go is relatively independent 

 of the transit time in the input space. 



Figure 21 shows the results of measurements on a triode identical with 

 that of Fig. 20 except that the grid consists of a mesh of 0.3 mil tungsten 

 wires wound at 550 strands per inch in both directions. It will be noted 



