[ARC5] Why "Noodling" About Sweep Tubes

[Kenneth G. Gordon]

On 26 Oct 2013 at 16:56, mac wrote:

> 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.

OK. Thanks for the info, Dennis. That makes things more clear.

> The 803 is a power pentode and I find no description of it as a "beam"
>  power tube in the literature.

Yes. I was actually looking at the data sheet for another tube when I wrote 
that....and I am so distracted by other things right now I can't even remember 
which one that was.

The RCA data sheet from HB-3 calls the 803 a "Power amplifier pentode" 
only.

My mistake.

Ken W7EKB