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

Cathode PuIsers: Hard-Tube Modulators (10) 179
r
Outer megnetic pole piece
Magnetically cmstrainad ~ Radial magnetic-field line
“.,., -,-
- Outer@d wirecircb
AZ CatJw3dawirecircle
9 Inner-gridwire circle
—-Inner
anode
Cross section through action spare, A-A
Figure 10-23. Construction of the type ML-8549 magnetically beamed hard-tube switch.
These synthesized points will be as useful to the designer as the original
published data, which are offered with no guarantee that they characterize any
given tube of the type. What, then, guarantees the performance for any tube
type, triode or tetrode? The guarantee lies within the specific quality-assurance
test specifications for a given tube type. These specifications are in one of two
formats: EIA or MIL-E-l. These specifications typically establish ranges of voltages
and/or currents within which a particular tube must fall in order to be sold
under its part number. For instance, the negative grid voltage required for the
plate current to be less than some specified value at a given anode voltage (or a
combination of anode and screen voltages) will not be expressed as a single value
but as a range of voltages. The transmitter design had better be able to accommodate
the entire range or the worst case. In other words, design to the tube
specification not the tube data sheets.
10.4.5 The ML-8549 magnetically beamed triode
The tubes discussed so far have used only geometry and electrostatics to
affect electron trajectories. The ML-8549 was one of the first attempts to use a
combination of geometric, electrostatic, and electromagnetic influences on electron
trajectories in order to maximize the number of them that make it to the
anode. The type 8549 triode is illustrated in Fig. 10-23. Note the cross-section
view of its inter-electrode action space. It is a radial-beam device. Its elements
are cylindrical and they are coaxial. The inner- and outermost elements, however,
are not electrodes at all. They are magnetic pole pieces whose orientation is
similar to those used in dynamic loudspeakers, in that they support radial magnetic
field lines. The space where the voice coil of a loudspeaker would fit is
occupied by the electrodes.
But this is no simple triode. There is a wire-type directly heated, thoriatedtungsten
cathode. But instead of being the innermost electrode, it is the centermost.
Inside and outside of it are two sets of wire control grids that are circurnferentially