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Re: Linear Amp for QRP

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  • Dave B
    I supose 180W is QRP for some.... If you re going to amplify a Softrock to that sort of level (52.55dBm or so) best make sure the unwanted image suppresion is
    Message 1 of 12 , Jun 1, 2012
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      I supose 180W is QRP for some....

      If you're going to amplify a Softrock to that sort of level (52.55dBm or
      so) best make sure the unwanted image suppresion is pretty darn good!

      Most modules of that ilk, at those low voltages will be in compression
      (not exactly "Linear") too, so take care.

      The heatsink looks barly adiquate too, unless you've got a good blower.
      OK for low duty cycle stuff I guess.

      Should be OK, clean/linear, and rugged (VSWR tollerant) at 50W or so, so
      long as you have good (FAST!) over current protection on the DC supply.

      Remember, power is nothing without control!

      Regards.

      Dave G0WBX.
    • John Rabson
      ... And a power semicondictor is the fastest fuse known to man. John F5VLF
      Message 2 of 12 , Jun 1, 2012
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        On 1 Jun 2012, at 22:45CEST, Dave B wrote:

         


        Should be OK, clean/linear, and rugged (VSWR tollerant) at 50W or so, so
        long as you have good (FAST!) over current protection on the DC supply.

        And a power semicondictor is the fastest fuse known to man.

        John F5VLF

      • Lawrence Galea
        Fastest fuse on three legs Regards Lawrence ________________________________ Da: John Rabson A: softrock40@yahoogroups.com Inviato:
        Message 3 of 12 , Jun 2, 2012
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          Fastest fuse on three legs
          Regards
          Lawrence


          Da: John Rabson <john.rabson@...>
          A: softrock40@yahoogroups.com
          Inviato: Sabato 2 Giugno 2012 7:36
          Oggetto: Re: [softrock40] Re: Linear Amp for QRP

           
          On 1 Jun 2012, at 22:45CEST, Dave B wrote:

           

          Should be OK, clean/linear, and rugged (VSWR tollerant) at 50W or so, so
          long as you have good (FAST!) over current protection on the DC supply.

          And a power semicondictor is the fastest fuse known to man.

          John F5VLF



        • Jasmine Strong
          Not quite as fast as a laserdiode. Spikes as short as 2 ns can destroy a laserdiode. -J.
          Message 4 of 12 , Jun 2, 2012
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            Not quite as fast as a laserdiode. Spikes as short as 2 ns can destroy a laserdiode.

            -J.

            On 2 Jun 2012, at 12:59, Lawrence Galea wrote:

             

            Fastest fuse on three legs
            Regards
            Lawrence


            Da: John Rabson <john.rabson@...>
            A: softrock40@yahoogroups.com
            Inviato: Sabato 2 Giugno 2012 7:36
            Oggetto: Re: [softrock40] Re: Linear Amp for QRP

             
            On 1 Jun 2012, at 22:45CEST, Dave B wrote:

             

            Should be OK, clean/linear, and rugged (VSWR tollerant) at 50W or so, so
            long as you have good (FAST!) over current protection on the DC supply.

            And a power semicondictor is the fastest fuse known to man.

            John F5VLF





          • Dave B
            Oh yes!... How fast a power semi self destructs, is directly proportional to the cost x diffulty of it s replacement! Protection is everything! The use of
            Message 5 of 12 , Jun 3, 2012
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              Oh yes!...

              How fast a power semi' self destructs, is directly proportional to the
              cost x diffulty of it's replacement!

              Protection is everything! The use of active current limiting/foldback
              on the DC supply, is just as esential as active monitoring of both
              forward and reflected power levels, with any needed warnings, trips, or
              automatic drive level reduction under extreme load VSWR contitions.

              It's especially a problem when such amps are driving very low impedances
              (as the devices "see" them) the currents developed rise scarily fast.
              That coupled with transmission line effects due to standing waves can
              result in an instant device failure, if something goes "open circuit"
              somewhere downstream. (1/4 wave transformer effects...)

              A solid state RF PA, is in essance a controled voltage generator, with
              (relatively) uncontroled currents. (DC and RF!) Yes, the device
              controls current itself, but under normal conditions that current is also
              a function of the DC input voltage and output load impedance, as "seen"
              by the PA stage. If the dynamic working point of the device stray's out
              of the "Safe Operating Area" into Secondary Breakdown teretory, the rest
              as they say is history. And very fast too.

              A Tube amp by comparison, is a controled current source, that can
              withstand (in the most part) high voltages under fault conditions, so can
              be less problematical, though not always in narrowband configurations,
              and especially not at VHF, where its often other parts that fail first,
              not the tube itself. (Cap's flashing over etc.)

              Tubes tend not to fail "Instantly" for the most part (if the amp is
              correctly designed for the tube in use) but give enough warning to the
              user that something is wrong by way of real time meetering in sight of
              the operator. But of course, the operator needs to know how to
              interperate those readings, and keep an eye on them. There are some
              commercial tube amps that automate all that, some better than others.

              I have yet to see even a commercial solid state PA, that has DC input
              current meetering, though often Fwd and Refl power metering is included.

              73

              Dave G0WBX.
            • Alex
              ... I have a ensemble rxtx and I built a kit amp from http://www.golddredgervideo.com/kc0wox/wa2ebyamp/ Take a look at this amp 40w out with 1w in. It works
              Message 6 of 12 , Jun 3, 2012
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                --- In softrock40@yahoogroups.com, Bruce Tanner <bet110@...> wrote:
                >
                > The thought did cross my mind!
                >
                > On 5/31/2012 3:40 PM, MIKE DURKIN wrote:
                > >
                > > With a pair of 2sc2879's .... 120w each .... id guess more are sold to
                > > CB'rs than hams ...
                > >
                > > -----Original Message-----
                > >
                > > From: Mike WA8BXN
                > > Sent: 31 May 2012 16:34:31 GMT
                > > To: softrock40@yahoogroups.com
                > > Subject: Re: [softrock40] Linear Amp for QRP
                > >
                > > It looks like it lacks bandpass filters.
                > >
                > >
                > >
                > >
                > > -------Original Message-------
                > >
                > > From: k2bet1
                > > Date: 5/31/2012 11:32:24 AM
                > > To: softrock40@yahoogroups.com <mailto:softrock40%40yahoogroups.com>
                > > Subject: [softrock40] Linear Amp for QRP
                > >
                > >
                > > I wonder if anyone has looked more closely at this amp? No affiliation
                > > just
                > > wondering what you think. Looks a bit like the Tokyo Hy-Power HL-45B.
                > >
                > > http://www.ebay
                > > com/itm/SSB-CW-HF-LINEAR-AMP-180W-QRP-SDR-817s-/150805937814?_trksid=p4340
                > > m1374&_trkparms=algo%3DUPI
                > > GIROS%26its%3DI%252BC%252BS%26itu%3DUCI%252BUCC%26otn%3D13%26pmod%3D290718831
                > > 68%26ps%3D63%26clkid%3D8806789656698524272
                > >
                > > bet
                > >
                > >
                > >
                > >
                > >
                > >
                > > __________ Information from ESET Smart Security, version of virus
                > > signature database 7185 (20120531) __________
                > >
                > > The message was checked by ESET Smart Security.
                > >
                > > http://www.eset.com
                >Hi Bruce,

                I have a ensemble rxtx and I built a kit amp from http://www.golddredgervideo.com/kc0wox/wa2ebyamp/
                Take a look at this amp 40w out with 1w in. It works absolutely beautiful with the softrock ensemble rxtx. I get about 45w out and everyone tells me how great it sound.
                You can easily get all parts from mouser or digikey.
                There is a link on the arrl article for this amp on where to get the printed circuit boards. Not hard to build at all.

                Good luck W6ACT
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