[Boatanchors] SWEEP TUBES AND FPM 300S

[Rob Atkinson]

Liles, if you knew all this then why did you ask me your question
about sweep tubes.

Rob
K5UJ

On Sun, Jan 10, 2016 at 5:28 PM, Jim Liles
<hallicrafterssr2000 at k9axn.com> wrote:
> John,
>
> Sweep tubes are beam power Tetrodes just like the 6146.  Neither has a
> suppressor grid just side director plates.  As for rugged, don't know of any
> 6146 pair running 550 watts SSB and 350 CW with 275 out SSB and 175 CW.
>
> IMD will be -30db and they are not as delicate as most think.  The tube is a
> 6KD6.
>
> If you ran a pair of 6KD6's at the same power level that 6146B' run, you
> would not need a blower.  The SR-400A uses a pair of 6KD6's but added a
> blower because it runs 500 watts in SSB.
>
> The notion that sweep tubes are inferior to the 6146 is simply misguided.
> They are actually superior
>
> If you look at the grid structure in the 6146 and sweep tubes you will find
> the same precision regarding the precise alignment of the control and screen
> grid that make beam power tubes the great performers they are.
>
> I'll upload images of the 6146, 8122, and 6KD6 construction so you can see
> for yourself what they are.  The control grid and screen are precisely
> aligned.  If you look toward the cathode from the screen you will see only
> control grid and from the control grid to plate you will see nothing but
> screen.
>
> The other sweep tubes are also Beam power tetrodes.  The tube layout in the
> data sheets would have you think they have a suppressor grid attached to the
> directors but it is not so --- none do.  Beam power tubes need no suppressor
> grid.  Also a Beam power tube like the 8122 is a tetrode also needing no
> suppressor or director plates because of tube geometry.
>
>