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

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Cathode Pulsers: Hard-Tube Modulators (10) 181 i Section view Figure 10-25. Type ML-8618 magnetically beamed triode switch tube. tivegrid voltage that produces 1100-A peak-platecurrent before (about +2700 V), nowproduces only 10-Apeak-grid current. The ratio is 110:1. More than 99%of the cathode current makes it to the anodes. However, the negative grid voltage required for plate-curnmt cutoff at 65 kV anode voltage is 4000 V, meaning that the amplification factor is only slightly more than 15. The total grid swing, therefore, is almost 7000 V. Even so, a peak-pulse output power of almost 65 MW is obtained from a drive power of approximately 100 kW.
182 High-Power Microwave-Tube Transmitters 280 260 I 1 Plate current -0 - Grid current 7 240 I I / 1 6 220 200 1600 5 160 160 140 120 100 80 2 60 40 1 20 0 m I 1 I 1 1 1 4 0 12 34 5 6 7 6 9 10 Armte voltage(W) 0 Figure 10-26. Voltage/current relationships of ML-8618 tnode. The tube was not electrically small, either. It had filament power of over 14 kW (7.5 V at 1880 A), which is about 12 W/A of pulse-cathode emission, and an anode-average-power-dissipation rating of 500 kW. Another indication of the reduced grid heating is the maximum pulse duration rating of 0.1 second, or 100,000 p.s. (Remember that grid heating, not cathode emission, is the pulseduration limiting factor in a thoriated-tungsten filament switch tube.) This tube is spoken of in the past tense because the application for which it was primarily intended-a giant, experimental pulse modulator—was by no means an unqualified success, and the tube type itself suffered by association. The magnetically beamed concept, however, did not die with it. 10.4.6 The ML- 8618 magrzetically beamed triode This tube, as shown in Fig. 10-25, is a very close relative of the type 8549. The electromagnetic strategy is the same, but the geometry is planar instead of coaxially cylindrical. The effect on performance is quite similar, as shown in the voltage/ current relationships of Fig. 10-26. The tube has been rated at as much as 50 kV anode-voltage hold-off-although it rarely operated above 40 kV. Using the 50-
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