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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Cathode Pulsers: Hard-Tube Modulators (10) 175<br />
-50<br />
0<br />
/<br />
/<br />
r<br />
/<br />
e<br />
/<br />
4<br />
— 1 — — _M- _<br />
/— 120 A<br />
——— —— A —<br />
2<br />
-—- —— __ ____ ____ ____ _<br />
——— —. —— ——— __— 1<br />
‘W<br />
100<br />
60<br />
40<br />
20<br />
10<br />
hcde current —<br />
Screen current — —<br />
-150<br />
1<br />
0 10 20 30<br />
Anode vollage (k~<br />
Figure IO-19. Voltage/current relationships in S94000E tetrode switch tube for screen voltage of 1000 V.<br />
semen-cathode voltage.<br />
Many tetrode types (and triode types as well) are used as high-power hardtube<br />
modulator switches, although they wem not designed for such service. These<br />
tetrodes range in capacity from the 100-kW anode dissipation of the 4CW1OO,OOO<br />
right up to megawatt-dissipation tubes. They were originally intended for use in<br />
high-power broadcast transmitters or other high-power RF sources at frequencies<br />
through the HP band (but usually not above 50 MHz). In RF amplifier service, a<br />
dc anode voltage rating in the 20-kV range is common. This may seem inadequate<br />
for most hard-tube modulator service, and it probably is. The maximum<br />
instantaneous anode voltage that an RF amplifier experiences is nearly twice the<br />
dc component, however. Moreover, a tube that is rated for high-level amplitude<br />
modulation at 100?4opositive modulation will see a “de” or audio-frequency peak<br />
that is also twice the average anode voltage. (Remember that the peak instantaneous<br />
power from a 100%-amplitude-modulated power amplifier is four times<br />
the carrier power, and even a 50-kW-rated transmitter produces 200-kW peak<br />
envelope power.) It can be seen that in modulator-switch service, where maximum<br />
voltage hold-off occurs during nominally zero-current situations, the true<br />
voltage-hold-off capability may be many times the RF-amplifier dc anode-voltage<br />
rating. This is especially true if the tube is specified at procurement for such<br />
service. In such cases, it can be specially processed during manufacture to enhance<br />
high-voltage tolerance.<br />
Two good examples of tetrodes designed expressly for service as high-voltage<br />
modulator switch tubes and intrapulse voltage regulators-and not just specially<br />
processed RF amplifier tubes-are<br />
the S94000Eand the 4CPW1OOOKB. The
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