3.6M north10.pdf - Dean-O's Toy Box

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Cathode Pulsers: Hard-Tube Modulators (10) 173
group of rods that has been placed on the same radials as the control-grid rods.
The shield rods are located just on the anode side of the control grid on a circle of
slightly larger diameter. The shield grid is connected to the cathode. Figure 10-
16 shows the normally concentric electrode assemblies lying side by side. Instead
of a uniformly emitting cathode surface, the 6544 has a number of individual
electrostatically focused electron guns cylindrically arrayed. M geometry
“hides” the control grid from the cathode as much as possible in a high-p
tube.
To what extent does this strategy succeed? The anode-voltage rating of the
6544 is 20 kV. Using the same 90%-efficiency criterion, at an anode voltage of 2
kV and a peak-grid voltage of 1300 V, the peak-anode current is 70 A and the grid
current is 5.5A, as shown in the current/voltage characteristics of Fig. 10-17. The
ratio is almost 13, which is certainly not bad for a tube with p. of 90. Total
cathode current is 75.5A, which is approximately the peak rating of the tube. Of
this, 93!40 is anode current and 770 is grid current. The filament heating power is
360 W, giving an emission loading of 4.8 W/A.
10.4.4 The S94000E and 4CPWIOOOKB tetrode switch tubes
The ML-6544 is a triode in that only three electrodes are externally accessible.
There is, however, a fourth electrode, the shield grid, but it operates at the same
voltage as the cathode and is internally connected to it. A true tetrode has an
independently operated fourth electrode, which is physically similar to the 6544
shield-grid and is typically operated at a continuously applied (or sometimes
pulsed) voltage positive with respect to the cathode, usua-lly in the range beu
● P-I wStiV13 grki-cathcca voltage
-Culam —
wcUmlM ---------
0 2 4 6 8 10
Anode voltage (k~
u
o 2 4 6 8 10
Anode voltaga (kV)
Figure 10-17. Voltage/currentcharacteristicsof type6544shield-grid tnode switch tube.