[Boatanchors] SWEEP TUBES AND FPM 300S

[Jim Liles]

Hi Rob,

Your comment regarding sweep tubes in the FPM300, and as long as they are 
used in TV sets, sounded a lot like you had found some problem with them. 
Wasn't a challenge.  There may be something I missed in the nature of those 
tubes.  Always open to new ideas.

You have to admit there's a lot of bad press regarding sweep tubes in ham 
gear.

Here's a link to some photos of beam power tubes.  No wording wrapped around 
them yet but the second photo of the 8122 has some narration. 
http://k9axn.com/_mgxroot/page_10886.html

No harm meant and If it was offensive --- my apologies.

Please have a great day Rob Kindest regards Jim K9AXN

-----Original Message----- 
From: Rob Atkinson
Sent: Sunday, January 10, 2016 7:45 PM
To: Jim Liles
Cc: W4AWM at aol.com ; Boat Anchors List
Subject: Re: [Boatanchors] SWEEP TUBES AND FPM 300S

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.
>
>