misread my own table...see correction below
----- Original Message -----
From: "jeff millar" <jeff@wa1hco.mv.com>
To: "sm5ki" <sm5ki@algonet.se>; <amps@contesting.com>
Sent: Sunday, October 29, 2000 2:52 PM
Subject: Re: [AMPS] Portable linear using a DAF?
>
> comments included below
>
> ----- Original Message -----
> From: "sm5ki" <sm5ki@algonet.se>
> To: <amps@contesting.com>
> Sent: Sunday, October 29, 2000 4:53 AM
> Subject: [AMPS] Portable linear using a DAF?
>
>
> >
> > Hej all:
> >
> > I want to collect together a light weight and compact ( low profile to
get
> > into a normal suit case) shortwave station for portable use including a
> > light weight linear that I have to build myself. Here my thoughts and
your
> > comments are most welcome:
> >
> > 1. Where do I find a light weight HV power supply and why are there no
> > switched power supplies for 2 -3 kV?
>
> Key design problems include
> - transformer resonates below switching frequency due to high
> capacitance in
> large number of turns required
> - slow switching speed of high voltage diodes
> >
> > 2. As alternative use a number of paralell cheap russian TV sweep tubes
> > with filaments in series to get rid of the filament transformer weight.
> Use
> > voltage qudrupling straight from 230 VAC mains with a well isolated
> chassie
> > to avoid electrical chocks. At the expected 500 W level use an outdoor
> 500W
> > SMART TUNER and a long wire.
>
> Creating a low voltage, low impedance output has a number of advantages.
> Consider getting the parallel plate impedance down to 200 ohms and then
> you can use a 4:1 toroidal transformer to match to 50 Ohms. This
> creates a broadband, no tune amp suitable for external antenna tuners.
> Don't forget the harmonic filter.
>
> Some calculations on place impedance, voltage and current:
>
> Rp = Ep / (Ip x 1.5) or Ip = Ep / (Rp x 1.5)
>
> Rp Ep Ip W
> 300 300 .67 200
> 300 450 1.0 450
> 300 600 1.5 900
> 200 300 1.0 300
> 200 450 1.5 675
> 200 500 1.7 800
> 200 600 2.0 1200
> 100 300 2 600
> 100 450 3 1350
>
> Looking at the 6KD6 data sheet, it looks like 150 ma max plate current
> which implies 10 in parallel at 450V yeilds 200 ohm plate impedance
> and can produce 675W.
Oops...need better proof reading skills. At 450V, that's 1.0A and about
6 tubes in parallel for 450W. Or with a bit more agressive power supply,
600V, 10 tubes in parallel, for 900W out.
>
> Just using a voltage multiplier off the mains will create very narrow
> high current spikes on the mains, leading to worse regulation that
expected
> and lots of HF noise in the environment.
>
> But eliminating the plate transformer has appealed to me for quite some
> time. Here's some things to think about
> - RF deck will have to float with respect to safety ground
> - Fullwave rectify the AC line and generate 300 VDC
> - Use a little bit of filter caps to fill in the nulls in the ripple
> - Use a boost type switching regulator and chop the AC line at 20-100
> KHz
> This broadens the current surges, improves power factor
> - Boost the voltage to 450V or so.
> - Put filter caps on the output, sized to eliminate the switching
> ripple
>
> Use a buck type switching regulator to produce the filiment voltage,
> probably can purchase off the shelf to do the job.
>
> > 3. Alternative would be a number paralellt 8072 tubes cooled with flat
> > volume blowers. Then I get the additional weight of the filament
> > transformer, of course.
>
> Way too expensive, too high an impedance, too much plate voltage
> >
> > 3. Use a DAF that dissipates less heat and requires less cooling and
> weight.
> > Which may mean a number of flat light weight computer type blowers.
>
> With a low voltage plate supply and sweep tubes, just generate a regulated
> screen supply.
>
> > 4. I know there have been similar linears on the market but they are too
> > heavy.
> >
> > 5. Transistorised linears are out as the cooler adds weight although a
> > switched power supply is OK.
> >
> > 6. A heavier alternative would be a heavier GU 74 DAF with my QRO HV
> toroid
> > transformer. The tubes are very cheap in Europe and reliable.
> >
> > 73s de Hans SM5KI
> >
> > --
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> > Problems: owner-amps@contesting.com
> >
> >
>
>
> --
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>
>
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