[Boatanchors] SWEEP TUBES AND FPM 300S

[Bry Carling]

I have a large box of sweep tubes available very chepa if someone might enjoy experimenting or building RF finals with them.

Brian AF4K

> To: boatanchors at mailman.qth.net
> From: wrcromwell at gmail.com
> Date: Mon, 11 Jan 2016 07:41:25 -0500
> Subject: Re: [Boatanchors] SWEEP TUBES AND FPM 300S
> 
> Hi John,
> 
> I use smaller sweep tubes and I use them at 20 to 30 watts. I attempt to 
> run them in class AB1 (linear) for the lower driving power requirement 
> (and the linearity helps, too). I use them for CW. Mostly they are 
> loafing along.
> 
> Some time ago there was a "Quarter Kilowatt" (250 watts *input*) 
> transmitter project in the ARRL Handbook(s) that uses a pair of 6KD6s.
> 
> I also use 6146s including the B model. Don't waste a lot of time tuning 
> them up either. Go for a plate dip *immediately* and continue tuning 
> from there. Otherwise invite the little crinkle noise followed by smoke.
> 
> 73,
> 
> Bill  KU8H
> 
> 
> On 01/10/2016 06:28 PM, Jim Liles 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.
> >
> > A super day to you Kindest Regards Jim K9AXN
> >
> > -----Original Message----- From: John via Boatanchors
> > Sent: Sunday, January 10, 2016 2:41 PM
> > To: boatanchors at mailman.qth.net
> > Subject: [Boatanchors] SWEEP TUBES AND FPM 300S
> >
> >
> > The industry switched to sweep tubes largely as an economic measure. They
> > were very cheap as compared to a heavy duty beam power tube such as the
> > 6146.  Some operated at lower plate current which made transformers 
> > cheaper.
> > They  would last much longer if they were air cooled and tune up 
> > periods were
> > kept  short which many ignored.  The best way I found to tune a sweep 
> > rig,
> > especially when tune up periods were extensive due to an antenna 
> > tuner, was
> > to  keep the drive low until the final seconds of the tune up period.
> >
> > I have three FPMs in the collection, The main weak link in the rig, in
> > addition to sweep tubes and slightly unstable VFO was the drive belt.
> > Fortunately, a repro belt is readily available.
> >
> > 73,
> >
> > John, W4AWM
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