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

176 High-Power Microwave-Tube Transmitters
0 -20 40 -60 -60 -1oo -120 -140 -16a
Grid VOl@E ~
Figure 10-20. Transfer characteristic for S94000E tetrode showing “projected” cutofi
.
S94000E has an anode-hold-off voltage rating of 200 kV and a maximum peakanode
current of 125A. (We will later see that peak-anode current is virtually the
same as the peak-cathode current.) The 4CPW1OOOKB has an anode-voltage
rating of 175 kV and a peak-anode-current rating of 75 A. Both tube types
evolved from high-power RF amplifier forebears. Like most tubes intended for
high-voltage hold-off capability, they differ from their predecessors in the spacing
between anode and screen grid. Consequently the slope of their diode, or
virtual-cathode, lines also differ.
The 4CPW1OOOKB is a radial-beam, external-anode tetrode of more-or-less
conventional geometry. It descended from the 4CW250000 and was intended
primarily as a megawatt-class RF amplifier in the HF band. Its anode is capable
of 1 MW of average dissipation— which is what the “1OOOK“ in its type designation
refers to-giving it extended capability for linear voltage nqydation and
waveform shaping.
The S94000E, by comparison, is literally inside out, as shown in Fig. 10-18. It
is a radial-beam tube, but its cylindrically shaped anode is on the inside of the
tube rather than the outside. Around the outer periphery is a circular array of
“unitized” electron guns, which are shown conceptually in the figure. Each gun
has its own central cathode bar, grid box, and screen box. The grid and scxeen
boxes are solid on three sides. The sides facing the anode are open, except for the
very fine wires stretched across them that are the actual control and screen ~ids.