3.6M north10.pdf - Dean-O's Toy Box
3.6M north10.pdf - Dean-O's Toy Box
3.6M north10.pdf - Dean-O's Toy Box
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174 High-Power Microwave-Tube Transmitters<br />
tween 1000 and 2000 V. This electrode shields; or “sc~ens,” the grid from the<br />
anode, so it is usually referred to as the screen grid. It is also placed very much<br />
closer to the control grid than to the anode. For all intents and purposes, themfore,<br />
the screen grid is a virtual anode to the control grid, operating at constant<br />
voltage with respect to the cathode. If positive control-grid-to-cathode voltage is<br />
requi~d for the desired peak-cathode emission (and it often is not), the amount<br />
of current intercepted by the grid for any fixed grid-cathode and screen-cathode<br />
voltages will be substantially independent of the anode-cathode voltage. Often,<br />
because of the electric-field strength at the cathode that results from screen-cathode<br />
voltage, full emission can be obtained with zero or even negative grid-cathode<br />
voltage, in which case there will be no grid power dissipation at all due to<br />
primary electron interception. However, the grid (and the screen as well) will be<br />
heated by radiation from the hot, nearby cathode.<br />
The amplification factor in a tetrode is defined with respect to the screen grid<br />
rather than the anode, as is the case with the triode. Tetrode amplification factors<br />
range typically from 5 to 10. Projected cathode-current cutoff occurs when a<br />
negative control-grid voltage, which is affected only slightly by the anode-cathode<br />
voltage, is applied that is between one-tenth to one-fifth of the positive<br />
\<br />
Sagnmt of Cyliirkal<br />
interior anode<br />
Swrnant of scrwn bbck _ ~<br />
Anode temllnsl<br />
I<br />
I<br />
-- Planaofcrosswctial<br />
Filsmanl, grid, and scrwn<br />
wnnacths<br />
Figure 10-18. Physical aspects of S94000E modulator switch tube.