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Re: [softrock40] Re: GM3SBC QRO Modifications

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  • Alan
    ... Subject: [softrock40] Re: GM3SBC QRO Modifications ... I see Ed says 4 BS170s need to be matched but surely the one used as a bias source is also best
    Message 1 of 15 , Mar 5 1:46 AM
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      ----- Original Message -----
      Subject: [softrock40] Re: GM3SBC QRO Modifications


      > Hi Alan
      >
      > Yes I have seen a wide variance in Gate Threshold Voltage in the devices I have tested. I have not however been able to translate
      > that into a measurable impact on power output, inter-modulation, harmonic content, or stability. As I noted, I defer to Ed based
      > on his extensive testing but I would be interested to know if anyone has observed any measurable operating impact from this
      > variance.
      >


      I see Ed says 4 BS170s need to be matched but surely the one used as a bias source is also best matched?

      The last instance of bad matching was due to a mis-matched Q5, causing the bias to be so low it cut off the PA devices. If all are
      matched then the bias should be correct without requiring any adjustment.
      And maybe no change to R41?

      I cannot comment on the tolerable amount of mis-match, I'd guess a BS170 might be non-linear if it were cut off with no drive?

      73 Alan G4ZFQ
    • warrenallgyer
      It remains a controversial subject.... I have not seen any evidence of the need but I am sure willing to be proven wrong. One possible weakness with Ed s
      Message 2 of 15 , Mar 5 2:29 AM
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        It remains a controversial subject.... I have not seen any evidence of the need but I am sure willing to be proven wrong.

        One possible weakness with Ed's design, and a possible reason for worrying more about the match, is the added two PAs on the bottom of the board are not thermally coupled to the bias BS170. This thermal coupling is largely responsible for the temperature stability of the original design. As the temperature of the assembly rises the bias is adjusted to compensate so they do not run away. The bottom two FETs are not coupled and potentially, I suppose, could run away without the bias FET being aware. The forced air cooling should prevent this but it does not have the benefit of the closed loop that the original design has.

        As far as matching the bias FET.... I have posted my findings and opinions on that in the past and I have not had reason to change that position. To me it is "chicken soup"..... "it couldn't hurt".

        Warren Allgyer - W8TOD

        --- In softrock40@yahoogroups.com, "Alan" <alan4alan@...> wrote:
        >
        >
        > ----- Original Message -----
        > Subject: [softrock40] Re: GM3SBC QRO Modifications
        >
        >
        > > Hi Alan
        > >
        > > Yes I have seen a wide variance in Gate Threshold Voltage in the devices I have tested. I have not however been able to translate
        > > that into a measurable impact on power output, inter-modulation, harmonic content, or stability. As I noted, I defer to Ed based
        > > on his extensive testing but I would be interested to know if anyone has observed any measurable operating impact from this
        > > variance.
        > >
        >
        >
        > I see Ed says 4 BS170s need to be matched but surely the one used as a bias source is also best matched?
        >
        > The last instance of bad matching was due to a mis-matched Q5, causing the bias to be so low it cut off the PA devices. If all are
        > matched then the bias should be correct without requiring any adjustment.
        > And maybe no change to R41?
        >
        > I cannot comment on the tolerable amount of mis-match, I'd guess a BS170 might be non-linear if it were cut off with no drive?
        >
        > 73 Alan G4ZFQ
        >
      • Sid Boyce
        Hi Warren, Looks like an alternative could be to mount the 4 FET s on a separate larger heatsink with 3 short leads from each pair to the board to address the
        Message 3 of 15 , Mar 5 6:17 AM
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          Hi Warren,
          Looks like an alternative could be to mount the 4 FET's on a separate larger heatsink with 3 short leads from each pair to the board to address the thermal issue? Ferrite beads on the gates?
          73 ... Sid.

          On 05/03/13 10:29, warrenallgyer wrote:
           

          It remains a controversial subject.... I have not seen any evidence of the need but I am sure willing to be proven wrong.

          One possible weakness with Ed's design, and a possible reason for worrying more about the match, is the added two PAs on the bottom of the board are not thermally coupled to the bias BS170. This thermal coupling is largely responsible for the temperature stability of the original design. As the temperature of the assembly rises the bias is adjusted to compensate so they do not run away. The bottom two FETs are not coupled and potentially, I suppose, could run away without the bias FET being aware. The forced air cooling should prevent this but it does not have the benefit of the closed loop that the original design has.

          As far as matching the bias FET.... I have posted my findings and opinions on that in the past and I have not had reason to change that position. To me it is "chicken soup"..... "it couldn't hurt".

          Warren Allgyer - W8TOD

          --- In softrock40@yahoogroups.com, "Alan" wrote:
          >
          >
          > ----- Original Message -----
          > Subject: [softrock40] Re: GM3SBC QRO Modifications
          >
          >
          > > Hi Alan
          > >
          > > Yes I have seen a wide variance in Gate Threshold Voltage in the devices I have tested. I have not however been able to translate
          > > that into a measurable impact on power output, inter-modulation, harmonic content, or stability. As I noted, I defer to Ed based
          > > on his extensive testing but I would be interested to know if anyone has observed any measurable operating impact from this
          > > variance.
          > >
          >
          >
          > I see Ed says 4 BS170s need to be matched but surely the one used as a bias source is also best matched?
          >
          > The last instance of bad matching was due to a mis-matched Q5, causing the bias to be so low it cut off the PA devices. If all are
          > matched then the bias should be correct without requiring any adjustment.
          > And maybe no change to R41?
          >
          > I cannot comment on the tolerable amount of mis-match, I'd guess a BS170 might be non-linear if it were cut off with no drive?
          >
          > 73 Alan G4ZFQ
          >



          -- 
          Sid Boyce ... Hamradio License G3VBV, Licensed Private Pilot
          Emeritus IBM/Amdahl Mainframes and Sun/Fujitsu Servers Tech Support
          Senior Staff Specialist, Cricket Coach
          Microsoft Windows Free Zone - Linux used for all Computing Tasks
          
        • warrenallgyer
          Sid It could be.... but Ed is clearly no amateur at this and it may not be a problem. I would be willing to try it. My 30/20/17 build puts out 2.6 watts in
          Message 4 of 15 , Mar 5 6:29 AM
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            Sid

            It could be.... but Ed is clearly no amateur at this and it may not be a problem. I would be willing to try it. My 30/20/17 build puts out 2.6 watts in its' stock condition. I tried some destructive testing on it I put it in full-power, key down operation for an hour and logged the power output and current consumption on one minute intervals. It was remarkably stable and did not run away for the entire hour. I am willing to bet that Ed's design may do the same so long as the fan is running. If, for some reason, the fan stops then all bets are off. It will rely on the match between the FETs being close enough that the thermal coupling between the top-of-board FETs and the bias FET can control the bias. I have no way of predicting if this will work other than trying it. And, assuming it does work... then the key would be within what matching parameters?

            The original design is deceptively simple in appearance and very robust in operation. Ed's may be as well.... but it needs to be tested.

            Warren Allgyer - W8TOD


            --- In softrock40@yahoogroups.com, Sid Boyce <sboyce@...> wrote:
            >
            > Hi Warren,
            > Looks like an alternative could be to mount the 4 FET's on a separate
            > larger heatsink with 3 short leads from each pair to the board to
            > address the thermal issue? Ferrite beads on the gates?
            > 73 ... Sid.
            >
            > On 05/03/13 10:29, warrenallgyer wrote:
            > >
            > > It remains a controversial subject.... I have not seen any evidence of
            > > the need but I am sure willing to be proven wrong.
            > >
            > > One possible weakness with Ed's design, and a possible reason for
            > > worrying more about the match, is the added two PAs on the bottom of
            > > the board are not thermally coupled to the bias BS170. This thermal
            > > coupling is largely responsible for the temperature stability of the
            > > original design. As the temperature of the assembly rises the bias is
            > > adjusted to compensate so they do not run away. The bottom two FETs
            > > are not coupled and potentially, I suppose, could run away without the
            > > bias FET being aware. The forced air cooling should prevent this but
            > > it does not have the benefit of the closed loop that the original
            > > design has.
            > >
            > > As far as matching the bias FET.... I have posted my findings and
            > > opinions on that in the past and I have not had reason to change that
            > > position. To me it is "chicken soup"..... "it couldn't hurt".
            > >
            > > Warren Allgyer - W8TOD
            > >
            > > --- In softrock40@yahoogroups.com
            > > <mailto:softrock40%40yahoogroups.com>, "Alan" wrote:
            > > >
            > > >
            > > > ----- Original Message -----
            > > > Subject: [softrock40] Re: GM3SBC QRO Modifications
            > > >
            > > >
            > > > > Hi Alan
            > > > >
            > > > > Yes I have seen a wide variance in Gate Threshold Voltage in the
            > > devices I have tested. I have not however been able to translate
            > > > > that into a measurable impact on power output, inter-modulation,
            > > harmonic content, or stability. As I noted, I defer to Ed based
            > > > > on his extensive testing but I would be interested to know if
            > > anyone has observed any measurable operating impact from this
            > > > > variance.
            > > > >
            > > >
            > > >
            > > > I see Ed says 4 BS170s need to be matched but surely the one used as
            > > a bias source is also best matched?
            > > >
            > > > The last instance of bad matching was due to a mis-matched Q5,
            > > causing the bias to be so low it cut off the PA devices. If all are
            > > > matched then the bias should be correct without requiring any
            > > adjustment.
            > > > And maybe no change to R41?
            > > >
            > > > I cannot comment on the tolerable amount of mis-match, I'd guess a
            > > BS170 might be non-linear if it were cut off with no drive?
            > > >
            > > > 73 Alan G4ZFQ
            > > >
            > >
            > >
            >
            >
            > --
            > Sid Boyce ... Hamradio License G3VBV, Licensed Private Pilot
            > Emeritus IBM/Amdahl Mainframes and Sun/Fujitsu Servers Tech Support
            > Senior Staff Specialist, Cricket Coach
            > Microsoft Windows Free Zone - Linux used for all Computing Tasks
            >
          • warrenallgyer
            Sid Off my soapbox and responding directly to your suggestion: for the original design concept to work you need would need to tightly couple the 4 PAs and the
            Message 5 of 15 , Mar 5 7:10 AM
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              Sid

              Off my soapbox and responding directly to your suggestion: for the original design concept to work you need would need to tightly couple the 4 PAs and the bias FET. The key to the original circuit is the tight thermal coupling between the PAs and the bias FET. Once I realized this I took each of mine apart and applied a THIN layer of thermal grease on the backside of the heatsink. The bias FET must "feel the pain" of the two PAs in order to be stable under extended periods of high load.... like WSPR operations.

              Under full load the negative feedback generated by the source resistance, together with the thermal adjustment of the bias, makes a very stable circuit. The two botom side PAs in the QRO design operate outside this thermal feedback loop and rely on air flow to keep them under control. This SHOULD work.... but they have no way to protest if it does not.

              Warren Allgyer - W8TOD

              --- In softrock40@yahoogroups.com, Sid Boyce <sboyce@...> wrote:
              >
              > Hi Warren,
              > Looks like an alternative could be to mount the 4 FET's on a separate
              > larger heatsink with 3 short leads from each pair to the board to
              > address the thermal issue? Ferrite beads on the gates?
              > 73 ... Sid.
              >
              > On 05/03/13 10:29, warrenallgyer wrote:
              > >
              > > It remains a controversial subject.... I have not seen any evidence of
              > > the need but I am sure willing to be proven wrong.
              > >
              > > One possible weakness with Ed's design, and a possible reason for
              > > worrying more about the match, is the added two PAs on the bottom of
              > > the board are not thermally coupled to the bias BS170. This thermal
              > > coupling is largely responsible for the temperature stability of the
              > > original design. As the temperature of the assembly rises the bias is
              > > adjusted to compensate so they do not run away. The bottom two FETs
              > > are not coupled and potentially, I suppose, could run away without the
              > > bias FET being aware. The forced air cooling should prevent this but
              > > it does not have the benefit of the closed loop that the original
              > > design has.
              > >
              > > As far as matching the bias FET.... I have posted my findings and
              > > opinions on that in the past and I have not had reason to change that
              > > position. To me it is "chicken soup"..... "it couldn't hurt".
              > >
              > > Warren Allgyer - W8TOD
              > >
              > > --- In softrock40@yahoogroups.com
              > > <mailto:softrock40%40yahoogroups.com>, "Alan" wrote:
              > > >
              > > >
              > > > ----- Original Message -----
              > > > Subject: [softrock40] Re: GM3SBC QRO Modifications
              > > >
              > > >
              > > > > Hi Alan
              > > > >
              > > > > Yes I have seen a wide variance in Gate Threshold Voltage in the
              > > devices I have tested. I have not however been able to translate
              > > > > that into a measurable impact on power output, inter-modulation,
              > > harmonic content, or stability. As I noted, I defer to Ed based
              > > > > on his extensive testing but I would be interested to know if
              > > anyone has observed any measurable operating impact from this
              > > > > variance.
              > > > >
              > > >
              > > >
              > > > I see Ed says 4 BS170s need to be matched but surely the one used as
              > > a bias source is also best matched?
              > > >
              > > > The last instance of bad matching was due to a mis-matched Q5,
              > > causing the bias to be so low it cut off the PA devices. If all are
              > > > matched then the bias should be correct without requiring any
              > > adjustment.
              > > > And maybe no change to R41?
              > > >
              > > > I cannot comment on the tolerable amount of mis-match, I'd guess a
              > > BS170 might be non-linear if it were cut off with no drive?
              > > >
              > > > 73 Alan G4ZFQ
              > > >
              > >
              > >
              >
              >
              > --
              > Sid Boyce ... Hamradio License G3VBV, Licensed Private Pilot
              > Emeritus IBM/Amdahl Mainframes and Sun/Fujitsu Servers Tech Support
              > Senior Staff Specialist, Cricket Coach
              > Microsoft Windows Free Zone - Linux used for all Computing Tasks
              >
            • Sid Boyce
              Thanks Warren, It s worth a try so I ll have a closer look at it. Out of 10 BS170 s in the pack from RS Components only 3 matched closely within 0.01V and the
              Message 6 of 15 , Mar 5 8:53 AM
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                Thanks Warren,
                It's worth a try so I'll have a closer look at it.

                Out of 10 BS170's in the pack from RS Components only 3 matched closely within 0.01V and the 2 removed were in the same ball park.

                The spread on the 10 were 3.13V - 3.18V. Whether the 3.18V ones would be OK to mix with 3.13V is the question.
                73 ... Sid.
                 
                On 05/03/13 15:10, warrenallgyer wrote:
                 

                Sid

                Off my soapbox and responding directly to your suggestion: for the original design concept to work you need would need to tightly couple the 4 PAs and the bias FET. The key to the original circuit is the tight thermal coupling between the PAs and the bias FET. Once I realized this I took each of mine apart and applied a THIN layer of thermal grease on the backside of the heatsink. The bias FET must "feel the pain" of the two PAs in order to be stable under extended periods of high load.... like WSPR operations.

                Under full load the negative feedback generated by the source resistance, together with the thermal adjustment of the bias, makes a very stable circuit. The two botom side PAs in the QRO design operate outside this thermal feedback loop and rely on air flow to keep them under control. This SHOULD work.... but they have no way to protest if it does not.

                Warren Allgyer - W8TOD

                --- In softrock40@yahoogroups.com, Sid Boyce wrote:
                >
                > Hi Warren,
                > Looks like an alternative could be to mount the 4 FET's on a separate
                > larger heatsink with 3 short leads from each pair to the board to
                > address the thermal issue? Ferrite beads on the gates?
                > 73 ... Sid.
                >
                > On 05/03/13 10:29, warrenallgyer wrote:
                > >
                > > It remains a controversial subject.... I have not seen any evidence of
                > > the need but I am sure willing to be proven wrong.
                > >
                > > One possible weakness with Ed's design, and a possible reason for
                > > worrying more about the match, is the added two PAs on the bottom of
                > > the board are not thermally coupled to the bias BS170. This thermal
                > > coupling is largely responsible for the temperature stability of the
                > > original design. As the temperature of the assembly rises the bias is
                > > adjusted to compensate so they do not run away. The bottom two FETs
                > > are not coupled and potentially, I suppose, could run away without the
                > > bias FET being aware. The forced air cooling should prevent this but
                > > it does not have the benefit of the closed loop that the original
                > > design has.
                > >
                > > As far as matching the bias FET.... I have posted my findings and
                > > opinions on that in the past and I have not had reason to change that
                > > position. To me it is "chicken soup"..... "it couldn't hurt".
                > >
                > > Warren Allgyer - W8TOD
                > >
                > > --- In softrock40@yahoogroups.com
                > > , "Alan" wrote:
                > > >
                > > >
                > > > ----- Original Message -----
                > > > Subject: [softrock40] Re: GM3SBC QRO Modifications
                > > >
                > > >
                > > > > Hi Alan
                > > > >
                > > > > Yes I have seen a wide variance in Gate Threshold Voltage in the
                > > devices I have tested. I have not however been able to translate
                > > > > that into a measurable impact on power output, inter-modulation,
                > > harmonic content, or stability. As I noted, I defer to Ed based
                > > > > on his extensive testing but I would be interested to know if
                > > anyone has observed any measurable operating impact from this
                > > > > variance.
                > > > >
                > > >
                > > >
                > > > I see Ed says 4 BS170s need to be matched but surely the one used as
                > > a bias source is also best matched?
                > > >
                > > > The last instance of bad matching was due to a mis-matched Q5,
                > > causing the bias to be so low it cut off the PA devices. If all are
                > > > matched then the bias should be correct without requiring any
                > > adjustment.
                > > > And maybe no change to R41?
                > > >
                > > > I cannot comment on the tolerable amount of mis-match, I'd guess a
                > > BS170 might be non-linear if it were cut off with no drive?
                > > >
                > > > 73 Alan G4ZFQ
                > > >
                > >
                > >
                >
                >



                -- 
                Sid Boyce ... Hamradio License G3VBV, Licensed Private Pilot
                Emeritus IBM/Amdahl Mainframes and Sun/Fujitsu Servers Tech Support
                Senior Staff Specialist, Cricket Coach
                Microsoft Windows Free Zone - Linux used for all Computing Tasks
                
              • John Williams
                Ed, What is the motivation of changing the 2n2222 to a BS170? Does it offer an independent improvement or is it in conjunction with the piggybacking of the
                Message 7 of 15 , Mar 13 7:59 AM
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                  Ed,

                  What is the motivation of changing the 2n2222 to a BS170? Does it offer
                  an independent improvement or is it in conjunction with the piggybacking
                  of the main BS170 quad circuit? Looking to understand the design theory...

                  John - ke5ssh
                  On 3/4/2013 12:49 PM, Ed wrote:
                  > modifying the Softrock Ensemble RXTX to increase the TX RF Output Power

                  --

                  John Williams

                  KE5SSH - ham since 2007
                  WQKA523 - GMRS for family use on the farm
                • Adam Jacobs
                  Sorry to resurrect a very old thread, but I m interested in this as well. I noticed that the amplifier design theory is not described very well at all (if at
                  Message 8 of 15 , May 8, 2013
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                    Sorry to resurrect a very old thread, but I'm interested in this as well. I noticed that the amplifier design theory is not described very well at all (if at all) in the uploaded word document and I don't see any discussion in this email thread either. Is Ed still on the list to give a design theory explanation?

                    Thanks,
                     -73 Adam W7QI


                    On Wed, Mar 13, 2013 at 7:59 AM, John Williams <KE5SSH@...> wrote:
                     

                    Ed,

                    What is the motivation of changing the 2n2222 to a BS170? Does it offer
                    an independent improvement or is it in conjunction with the piggybacking
                    of the main BS170 quad circuit? Looking to understand the design theory...

                    John - ke5ssh
                    On 3/4/2013 12:49 PM, Ed wrote:
                    > modifying the Softrock Ensemble RXTX to increase the TX RF Output Power

                    --

                    John Williams

                    KE5SSH - ham since 2007
                    WQKA523 - GMRS for family use on the farm


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