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Re: [softrock40] How high can you safely push the voltage to on a Softrock RXTX?

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  • Chris Wilson
    ... 17/06/2013 16:34 I have read, but may have misunderstood, that running the output transistors at as high a voltage as they are able to tolerate will reduce
    Message 1 of 13 , Jun 17, 2013
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      >
      > It appears the component with the lowest voltage absolute maximum
      > rating is the 78L05 at 30 volts. I don't think I'd push it that far,
      > though. Is there a reason you want to go beyond 13.8 volts? That voltage would definitely be fine.

      > 73, Zack W9SZ





      17/06/2013 16:34

      I have read, but may have misunderstood, that running the output
      transistors at as high a voltage as they are able to tolerate will
      reduce IMD and / or increase power output at a given IMD level. I was
      curious as to how far it was prudent to go. I would use a well
      regulated supply if pushing the envelope, of course. Just learning
      really, would rather blow up a Softrock semiconductor or two than play
      with my Kenwood TS-590 :) Although my Elmer insists I should get
      inside it, add bigger fans and up the PA pair bias ;) Or buy what he
      calls a proper rig, which is either valved or with a 50 volt
      semiconductor PA circuit. He has a thing about IMD and it's catching!

      --
      Best Regards,
      Chris Wilson. 2E0ILY
    • warrenallgyer
      Hi Chris I think you can take your cue from the voltage rated components. The power supply caps are rated at 16v There is a school of thought (that I
      Message 2 of 13 , Jun 18, 2013
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        Hi Chris

        I think you can take your cue from the voltage rated components. The power supply caps are rated at 16v

        There is a school of thought (that I personally subscribe to) that you can run components safely at their rating.

        There is another school of thought that says to stay 10-15% below the ratings which would put you at 13.6.

        I have run mine for extended periods at 16V with no issues and with pretty remarkable power out and IMD.

        Warren Allgyer - 9V1TD

        --- In softrock40@yahoogroups.com, Chris Wilson <chris@...> wrote:
        >
        >
        >
        > 17/06/2013 15:22
        >
        > In the search for the best IMD I am *CONSIDERING* pushing the voltage
        > as high as safely possible to my Softrock Ensemble RXTX. Can anyone
        > suggest how high that might be please? Thanks.
        >
        > --
        > Best Regards,
        > Chris Wilson. 2E0ILY
        > mailto: chris@...
        >
      • warrenallgyer
        Remember too that the 12V power rail runs at 0.7V (junction drop of D4) below the supplied voltage. So cranking the power supply up to 16.7 would be the
        Message 3 of 13 , Jun 18, 2013
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          Remember too that the 12V power rail runs at 0.7V (junction drop of D4) below the supplied voltage. So cranking the power supply up to 16.7 would be the "maximum rated voltage".



          --- In softrock40@yahoogroups.com, "warrenallgyer" <allgyer@...> wrote:
          >
          > Hi Chris
          >
          > I think you can take your cue from the voltage rated components. The power supply caps are rated at 16v
          >
          > There is a school of thought (that I personally subscribe to) that you can run components safely at their rating.
          >
          > There is another school of thought that says to stay 10-15% below the ratings which would put you at 13.6.
          >
          > I have run mine for extended periods at 16V with no issues and with pretty remarkable power out and IMD.
          >
          > Warren Allgyer - 9V1TD
          >
          > --- In softrock40@yahoogroups.com, Chris Wilson <chris@> wrote:
          > >
          > >
          > >
          > > 17/06/2013 15:22
          > >
          > > In the search for the best IMD I am *CONSIDERING* pushing the voltage
          > > as high as safely possible to my Softrock Ensemble RXTX. Can anyone
          > > suggest how high that might be please? Thanks.
          > >
          > > --
          > > Best Regards,
          > > Chris Wilson. 2E0ILY
          > > mailto: chris@
          > >
          >
        • Alan
          ... Subject: [softrock40] Re: How high can you safely push the voltage to on a Softrock RXTX? ... Warren, I m starting yet another school of thought that says
          Message 4 of 13 , Jun 18, 2013
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            ----- Original Message -----
            Subject: [softrock40] Re: How high can you safely push the voltage to on a Softrock RXTX?


            > I think you can take your cue from the voltage rated components. The power supply caps are rated at 16v
            > There is a school of thought (that I personally subscribe to) that you can run components safely at their rating.
            > There is another school of thought that says to stay 10-15% below the ratings which would put you at 13.6.

            Warren,

            I'm starting yet another school of thought that says 10% overload will not materially affect the life of components:) Or how about
            20%? I'm not going to test but I reckon it could be true.

            But have a good smoke alarm..

            I suspect there is another school of thought that says it's not quite that simple. Is IMD the only thing to worry about?

            Personally I feel that we should err on the side of caution and not push things to the maximum.
            Something may check out well under test conditions but unless those test conditions include all eventualities, component tolerances,
            build variations, temperature, different load conditions, possible voltage drops etc etc.. can we guarantee a reasonably clean
            signal for the years ahead?

            >
            > I have run mine for extended periods at 16V with no issues and with pretty remarkable power out and IMD.

            Just one post saying that could prompt someone to say "if you can do so can I". Without any checks at all? There are enough bad
            signals on the bands already without encouraging more. A few here have indicated that they have not even monitored their
            transmissions, let alone tested them.
            Then the next thing is it gets into an amplifier..

            Yes, you and Chris are testing, but others may not get the same results.

            73 Alan G4ZFQ

            >>
            >> In the search for the best IMD I am *CONSIDERING* pushing the voltage
            >> as high as safely possible to my Softrock Ensemble RXTX. Can anyone
            >> suggest how high that might be please?
          • Chris Wilson
            ... 18/06/2013 20:04 With me it s more about playing with my new test gear and seeing how changes affect measurements, and indeed, seeing how to DO the
            Message 5 of 13 , Jun 18, 2013
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              > Warren,

              > I'm starting yet another school of thought that says 10% overload
              > will not materially affect the life of components:) Or how about
              > 20%? I'm not going to test but I reckon it could be true.

              > But have a good smoke alarm..

              > I suspect there is another school of thought that says it's not
              > quite that simple. Is IMD the only thing to worry about?

              > Personally I feel that we should err on the side of caution and not push things to the maximum.
              > Something may check out well under test conditions but unless those
              > test conditions include all eventualities, component tolerances,
              > build variations, temperature, different load conditions, possible
              > voltage drops etc etc.. can we guarantee a reasonably clean
              > signal for the years ahead?

              >>
              >> I have run mine for extended periods at 16V with no issues and with pretty remarkable power out and IMD.

              > Just one post saying that could prompt someone to say "if you can
              > do so can I". Without any checks at all? There are enough bad
              > signals on the bands already without encouraging more. A few here
              > have indicated that they have not even monitored their
              > transmissions, let alone tested them.
              > Then the next thing is it gets into an amplifier..

              > Yes, you and Chris are testing, but others may not get the same results.

              > 73 Alan G4ZFQ



              18/06/2013 20:04

              With me it's more about playing with my new test gear and seeing how
              changes affect measurements, and indeed, seeing how to DO the
              measurements in the first place. Rather than trying to pull the
              ultimate out of a Softrock RXTX. I was more curious as to whether
              raising the voltage reduced IMD, and by how much, rather than taking
              advantage of it at the bleeding edge of reliability. I am far more of
              a hands on sort of chap, than a text book chap. Once I SEE something
              work, and do the stuff myself I have a far better chance of retaining
              it, as opposed to just reading about it in a book. I find some of the
              better posters on YouTube a Godsend, as they know what they are doing
              and present it in a practical manner. Another Alan at:

              http://www.youtube.com/channel/UCiqd3GLTluk2s_IBt7p_LjA

              for example.


              --
              Best Regards,
              Chris Wilson. 2E0ILY
            • Alan
              ... Subject: Re: [softrock40] Re: How high can you safely push the voltage to on a Softrock RXTX? ... Chris, I know you are not pushing to the limit. I was
              Message 6 of 13 , Jun 18, 2013
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                ----- Original Message -----
                Subject: Re: [softrock40] Re: How high can you safely push the voltage to on a Softrock RXTX?


                >
                > With me it's more about playing with my new test gear and seeing how
                > changes affect measurements, and indeed, seeing how to DO the
                > measurements in the first place. Rather than trying to pull the
                > ultimate out of a Softrock RXTX.

                Chris,

                I know you are not pushing to the limit.
                I was having a playful dig at Warren, who is.
                I'd guess that higher voltage with no increase in drive should improve linearity. But maybe it's not that simple.

                73 Alan G4ZFQ
              • Jack Smith
                At least with respect to bipolar and junction FETs, the intermodulation performance is a function of idle current and all the devices I ve used and measured
                Message 7 of 13 , Jun 18, 2013
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                  At least with respect to bipolar and junction FETs, the intermodulation performance is a function of idle current and all the devices I've used and measured have an optimum idle current yielding the best 2nd and 3rd order distortion. (Which is not the same in each device bearing the same part number.)

                  Idle current above or below that optimum results in worse intermodulation performance. I don't use MOSFETs in my RF products so I can't speak from experience in that  regard, but I would not be surprised to find the same relationship.

                  I should also add that the idle current that optimizes 3rd order intermodulation is seldom - if ever - the same idle current that optimizes 2nd order distortion. Fortunately, in a push-pull RF circuit with a low pass filter, even order distortion is improved by the push pull arrangement and the output LP filter and can usually be disregarded.

                  Increasing operating voltage keeping the same bias arrangement will increase the idle current in most designs. This may move the 3rd order intermodulation performance closer to the "sweet spot" of maximum 3rd order intermodulation performance or it may move it further away from that point.

                  With respect to output power, increasing the supply voltage should allow a greater undistorted peak-to-peak voltage swing between clipping and saturation and hence increased output power.

                  Ideally one would combine increased supply voltage with judicious tweaks to the bias so as to maintain good 3rd order performance. Bias tweaks may or may not be required; depends on many factors, but it may be required.

                  As far as effects upon reliability I do not design any product to operate even close to the maximum design ratings. I also try to use the best reliability parts, e.g., 105 deg C electrolytic capacitors, not 85 deg C parts, with the thought of saving a few cents per product but increasing the purchaser's maintenance is  poor practice. On the other hand if you are tinkering and don't mind replacing parts every now and then in something you have built, those concerns are not determinative.

                  Or, since Chris is an internal combustion engine guy, I suspect he is familiar with the aphorism "you have to finish the race to win the race." Being in the lead for 90% of the laps and then having a blown head gasket isn't a good thing.

                  Jack K8ZOA


                  On 6/17/2013 11:39 AM, Chris Wilson wrote:
                   



                  >
                  > It appears the component with the lowest voltage absolute maximum
                  > rating is the 78L05 at 30 volts. I don't think I'd push it that far,
                  > though. Is there a reason you want to go beyond 13.8 volts? That voltage would definitely be fine.

                  > 73, Zack W9SZ

                  17/06/2013 16:34

                  I have read, but may have misunderstood, that running the output
                  transistors at as high a voltage as they are able to tolerate will
                  reduce IMD and / or increase power output at a given IMD level. I was
                  curious as to how far it was prudent to go. I would use a well
                  regulated supply if pushing the envelope, of course. Just learning
                  really, would rather blow up a Softrock semiconductor or two than play
                  with my Kenwood TS-590 :) Although my Elmer insists I should get
                  inside it, add bigger fans and up the PA pair bias ;) Or buy what he
                  calls a proper rig, which is either valved or with a 50 volt
                  semiconductor PA circuit. He has a thing about IMD and it's catching!

                  --
                  Best Regards,
                  Chris Wilson. 2E0ILY


                • warrenallgyer
                  (fully bandaged following Alan s dig) I actually attempted destructive testing with the RXTX. I was willing to sacrifice the finals and surrounding components
                  Message 8 of 13 , Jun 18, 2013
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                    (fully bandaged following Alan's dig)

                    I actually attempted destructive testing with the RXTX. I was willing to sacrifice the finals and surrounding components to see if I could make the radio go into thermal runaway. Bottom line is I could not.

                    I ran my 15/12/10 at 16 volts, full power test tone with 3.3 V P_P audio drive, for one hour. I logged total current consumption and power output at one minute intervals initially, and then when that got too boring, at 5 minute intervals.

                    The final heat sink assembly got too hot to touch, the current rose to about 110% of startup and then stabilized. The power output was quite high because of the 16V and drifted down maybe 10% then stabilized.

                    I let it go in that condition another 20 minutes beyond the hour, then shut it down. There was no detectable damage and I continue to use the rig today. It gave me a new degree of confidence in the reliability and respect for the design.

                    Regarding Alan's concern about me leading a newbie into a dark dungeon of destruction I offer this disclaimer:

                    If you operate the Softrocks within the ratings for which they are designed you will have a fun, reliable, compliant radio that will last a long time. If you push the limits you need to have instruments to assure you remain in compliance with the rules and a well-stocked spares drawer, just in case.

                    Warren Allgyer - 9V1TD

                    --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
                    >
                    >
                    > ----- Original Message -----
                    > Subject: Re: [softrock40] Re: How high can you safely push the voltage to on a Softrock RXTX?
                    >
                    >
                    > >
                    > > With me it's more about playing with my new test gear and seeing how
                    > > changes affect measurements, and indeed, seeing how to DO the
                    > > measurements in the first place. Rather than trying to pull the
                    > > ultimate out of a Softrock RXTX.
                    >
                    > Chris,
                    >
                    > I know you are not pushing to the limit.
                    > I was having a playful dig at Warren, who is.
                    > I'd guess that higher voltage with no increase in drive should improve linearity. But maybe it's not that simple.
                    >
                    > 73 Alan G4ZFQ
                    >
                  • Jack Smith
                    Thermal runaway is less of a problem with MOSFET than bipolar because the majority carrier mobility decreases with increasing temperature, unlike a BJT, where
                    Message 9 of 13 , Jun 18, 2013
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                      Thermal runaway is less of a problem with MOSFET than bipolar because the majority carrier mobility decreases with increasing temperature, unlike a BJT, where the Vbe decreases as temperature increases and hence thermal runaway can occur for fixed bias voltage operation.

                      You might also consider what happens to the drain voltage if operating into an open circuit at maximum power and maximum voltage. The higher the power supply voltage the greater the chance of exceeding the drain/source voltage rating of the device.

                      If always operated into a 50 ohm load, then no problem. But part of a check of good design practice is to operate into a short circuit and an open circuit at maximum drive and on the worst case frequency. Even better to verify proper operation with a range of load Z.



                      Jack K8ZOA

                      On 6/18/2013 8:01 PM, warrenallgyer wrote:
                       

                      (fully bandaged following Alan's dig)

                      I actually attempted destructive testing with the RXTX. I was willing to sacrifice the finals and surrounding components to see if I could make the radio go into thermal runaway. Bottom line is I could not.

                      I ran my 15/12/10 at 16 volts, full power test tone with 3.3 V P_P audio drive, for one hour. I logged total current consumption and power output at one minute intervals initially, and then when that got too boring, at 5 minute intervals.

                      The final heat sink assembly got too hot to touch, the current rose to about 110% of startup and then stabilized. The power output was quite high because of the 16V and drifted down maybe 10% then stabilized.

                      I let it go in that condition another 20 minutes beyond the hour, then shut it down. There was no detectable damage and I continue to use the rig today. It gave me a new degree of confidence in the reliability and respect for the design.

                      Regarding Alan's concern about me leading a newbie into a dark dungeon of destruction I offer this disclaimer:

                      If you operate the Softrocks within the ratings for which they are designed you will have a fun, reliable, compliant radio that will last a long time. If you push the limits you need to have instruments to assure you remain in compliance with the rules and a well-stocked spares drawer, just in case.

                      Warren Allgyer - 9V1TD

                      --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
                      >
                      >
                      > ----- Original Message -----
                      > Subject: Re: [softrock40] Re: How high can you safely push the voltage to on a Softrock RXTX?
                      >
                      >
                      > >
                      > > With me it's more about playing with my new test gear and seeing how
                      > > changes affect measurements, and indeed, seeing how to DO the
                      > > measurements in the first place. Rather than trying to pull the
                      > > ultimate out of a Softrock RXTX.
                      >
                      > Chris,
                      >
                      > I know you are not pushing to the limit.
                      > I was having a playful dig at Warren, who is.
                      > I'd guess that higher voltage with no increase in drive should improve linearity. But maybe it's not that simple.
                      >
                      > 73 Alan G4ZFQ
                      >


                    • warrenallgyer
                      Jack I cannot explain the phenomenon but I have observed very quick and devastating thermal runaway in the RXTX by breaking the thermal coupling between the
                      Message 10 of 13 , Jun 18, 2013
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                        Jack

                        I cannot explain the phenomenon but I have observed very quick and devastating thermal runaway in the RXTX by breaking the thermal coupling between the two finals and the bias regulator.....The third BS170 in the heat sink assembly. Without negative bias feedback from increased temperatures these finals will destroy themselves in a few minutes. I am particularly careful to maximize thermal coupling in among all three of these devices.

                        I have not tried operating the RXTX with no load at 16V but I have inadvertently done it for several minutes at 13.8 V with no ill effects.

                        --- In softrock40@yahoogroups.com, Jack Smith <Jack.Smith@...> wrote:
                        >
                        > Thermal runaway is less of a problem with MOSFET than bipolar because
                        > the majority carrier mobility decreases with increasing temperature,
                        > unlike a BJT, where the Vbe decreases as temperature increases and hence
                        > thermal runaway can occur for fixed bias voltage operation.
                        >
                        > You might also consider what happens to the drain voltage if operating
                        > into an open circuit at maximum power and maximum voltage. The higher
                        > the power supply voltage the greater the chance of exceeding the
                        > drain/source voltage rating of the device.
                        >
                        > If always operated into a 50 ohm load, then no problem. But part of a
                        > check of good design practice is to operate into a short circuit and an
                        > open circuit at maximum drive and on the worst case frequency. Even
                        > better to verify proper operation with a range of load Z.
                        >
                        >
                        >
                        > Jack K8ZOA
                        >
                        > On 6/18/2013 8:01 PM, warrenallgyer wrote:
                        > >
                        > > (fully bandaged following Alan's dig)
                        > >
                        > > I actually attempted destructive testing with the RXTX. I was willing
                        > > to sacrifice the finals and surrounding components to see if I could
                        > > make the radio go into thermal runaway. Bottom line is I could not.
                        > >
                        > > I ran my 15/12/10 at 16 volts, full power test tone with 3.3 V P_P
                        > > audio drive, for one hour. I logged total current consumption and
                        > > power output at one minute intervals initially, and then when that got
                        > > too boring, at 5 minute intervals.
                        > >
                        > > The final heat sink assembly got too hot to touch, the current rose to
                        > > about 110% of startup and then stabilized. The power output was quite
                        > > high because of the 16V and drifted down maybe 10% then stabilized.
                        > >
                        > > I let it go in that condition another 20 minutes beyond the hour, then
                        > > shut it down. There was no detectable damage and I continue to use the
                        > > rig today. It gave me a new degree of confidence in the reliability
                        > > and respect for the design.
                        > >
                        > > Regarding Alan's concern about me leading a newbie into a dark dungeon
                        > > of destruction I offer this disclaimer:
                        > >
                        > > If you operate the Softrocks within the ratings for which they are
                        > > designed you will have a fun, reliable, compliant radio that will last
                        > > a long time. If you push the limits you need to have instruments to
                        > > assure you remain in compliance with the rules and a well-stocked
                        > > spares drawer, just in case.
                        > >
                        > > Warren Allgyer - 9V1TD
                        > >
                        > > --- In softrock40@yahoogroups.com
                        > > <mailto:softrock40%40yahoogroups.com>, "Alan" <alan4alan@> wrote:
                        > > >
                        > > >
                        > > > ----- Original Message -----
                        > > > Subject: Re: [softrock40] Re: How high can you safely push the
                        > > voltage to on a Softrock RXTX?
                        > > >
                        > > >
                        > > > >
                        > > > > With me it's more about playing with my new test gear and seeing how
                        > > > > changes affect measurements, and indeed, seeing how to DO the
                        > > > > measurements in the first place. Rather than trying to pull the
                        > > > > ultimate out of a Softrock RXTX.
                        > > >
                        > > > Chris,
                        > > >
                        > > > I know you are not pushing to the limit.
                        > > > I was having a playful dig at Warren, who is.
                        > > > I'd guess that higher voltage with no increase in drive should
                        > > improve linearity. But maybe it's not that simple.
                        > > >
                        > > > 73 Alan G4ZFQ
                        > > >
                        > >
                        > >
                        >
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