[Milsurplus] [ARC5] Why "Noodling" About Sweep Tubes
mac
w7qho at aol.com
Sat Oct 26 19:56:45 EDT 2013
The electron "beams" in a beam tetrode are formed by a particular
alignment of the control and screen grid wires. In tubes like the
6L6, 807, etc., this alignment can be maintained only in the central
areas of the grid structures and beam formation is disrupted in the
areas on the sides where the grid supporting wires get in the way.
The "beam forming" plates found in these tubes serve to mask off from
the plate those areas on the sides of the grid structures where this
disruption of the beams takes place. The plates (which normally run
at cathode potential) are thus much more accurately described as beam
"confining" as opposed to beam "forming" structures. In other tubes
such as the 4-250, 4-400 and the like the grids are structured and
supported so as to allow full 360 degree beam formation without
obstruction, hence no confining plates or other such structures are
required.
The 803 is a power pentode and I find no description of it as a "beam"
power tube in the literature. If it were such there would be no need
for the suppressor grid (g3). No beam confining/conforming plates in
an 803 either as you point out.
Dennis D. W7QHO
Glendale, CA
**************
On Oct 25, 2013, at 8:04 PM, Kenneth G. Gordon wrote:
> Also, I have never really been able to understand why 803 is termed a
> "beam-power pentode". AFAIK, it has no "beam forming" plates.
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