Loading ...
Sorry, an error occurred while loading the content.

Re: To match or not to match... BS170s in your RXTX

Expand Messages
  • KF4BQ
    ... Hi Warren, Some bias point operation and other issues discussed at: http://groups.yahoo.com/group/softrock40/message/55570 73, Mike Collins KF4BQ
    Message 1 of 19 , Nov 30, 2012
    • 0 Attachment
      --- In softrock40@yahoogroups.com, "warrenallgyer" <allgyer@...> wrote:
      >
      > So variances in Q5 produce big variances in the Q6 drive level as well as the operating point of the finals. This is why the Q5 circuitry is so effective at stabilizing the finals and why a choice here affects the power performance of the radio.
      >
      > This is my analysis. Do you agree?
      >

      Hi Warren,

      Some bias point operation and other issues discussed at:
      http://groups.yahoo.com/group/softrock40/message/55570

      73, Mike Collins KF4BQ
    • Taka Sugi
      Hi Warren Yes, almost I agree. ... 1. Ib(Q4)= Id(Q5) - Vbe(Q4)/R41 Here Vbe(Q4) is about 0.6V 2. Ic(Q4)=hfe(Q4) x Ib(Q4) 3. Vbias= V1 - (R39 xIc(Q4) + Vd(D3))
      Message 2 of 19 , Dec 2, 2012
      • 0 Attachment
        Hi Warren

        Yes, almost I agree.

        > 1) As discussed, current through Q5 drives Q4 and effectively
        >reduces the resistance of R40. This lowers the bias level on
        >the finals.

        1. Ib(Q4)= Id(Q5) - Vbe(Q4)/R41
        Here Vbe(Q4) is about 0.6V
        2. Ic(Q4)=hfe(Q4) x Ib(Q4)
        3. Vbias= V1 - (R39 xIc(Q4) + Vd(D3))
        Here V1= S12v - (R37 xIbias-circuit + Ic(Q6))
        If Id(Q5) is increased, then Ic(Q4) is increased, as a result
        Vbias is decreased( goes down).

        If Id(Q7,Q8) goes up by temperature, then Id(Q5, thermally connected
        to Q7,Q8) also goes up and Vbias goes down, then Id(Q7,Q8) goes down.
        This is a kind of "feedback".
        I am not sure about the function of R40(22.1k-ohm),but I think this
        is to avoide "local oscillation"?

        > 2) The increased current through Q5 also increases the voltage
        > drop across R37 which reduces the collector voltage on Q6, the
        >2n2222 driver. This reduces the drive level to the finals, reducing
        >the power output.
        > So variances in Q5 produce big variances in the Q6 drive level as
        >well as the operating point of the finals. This is why the Q5
        >circuitry is so effective at stabilizing the finals and why a
        >choice here affects the power performance of the radio.
        >
        > This is my analysis. Do you agree?

        I think there is little influence to Ic of driver Tr:Q6(2N2222),
        unless Q5 varies drastically, because R37 is small ( 22.1 ohm).

        JA1TLH/Taka
      • Alan
        ... Subject: [softrock40] Re: To match or not to match... BS170s in your RXTX Taka, Did you read this? http://groups.yahoo.com/group/softrock40/message/55570
        Message 3 of 19 , Dec 3, 2012
        • 0 Attachment
          ----- Original Message -----
          Subject: [softrock40] Re: To match or not to match... BS170s in your RXTX


          Taka,

          Did you read this? http://groups.yahoo.com/group/softrock40/message/55570

          Mike points out that Q4 maintains a constant current through R41 and therefore through Q5.
          The current is constant in Q5, what varies is the voltage across it.
          This is passed to Q7/8 through D3.
          Q4 just maintains the constant current.

          Mike, are you there?

          73 Alan G4ZFQ



          > Yes, almost I agree.
          >
          >> 1) As discussed, current through Q5 drives Q4 and effectively
          >>reduces the resistance of R40. This lowers the bias level on
          >>the finals.
          >
          > 1. Ib(Q4)= Id(Q5) - Vbe(Q4)/R41
          > Here Vbe(Q4) is about 0.6V
          > 2. Ic(Q4)=hfe(Q4) x Ib(Q4)
          > 3. Vbias= V1 - (R39 xIc(Q4) + Vd(D3))
          > Here V1= S12v - (R37 xIbias-circuit + Ic(Q6))
          > If Id(Q5) is increased, then Ic(Q4) is increased, as a result
          > Vbias is decreased( goes down).
          >
          > If Id(Q7,Q8) goes up by temperature, then Id(Q5, thermally connected
          > to Q7,Q8) also goes up and Vbias goes down, then Id(Q7,Q8) goes down.
          > This is a kind of "feedback".
          > I am not sure about the function of R40(22.1k-ohm),but I think this
          > is to avoide "local oscillation"?
          >
          >> 2) The increased current through Q5 also increases the voltage
          >> drop across R37 which reduces the collector voltage on Q6, the
          >>2n2222 driver. This reduces the drive level to the finals, reducing
          >>the power output.
          >> So variances in Q5 produce big variances in the Q6 drive level as
          >>well as the operating point of the finals. This is why the Q5
          >>circuitry is so effective at stabilizing the finals and why a
          >>choice here affects the power performance of the radio.
          >>
          >> This is my analysis. Do you agree?
          >
          > I think there is little influence to Ic of driver Tr:Q6(2N2222),
          > unless Q5 varies drastically, because R37 is small ( 22.1 ohm).
        • Taka Sugi
          Hi Alan ... Yes, I knew. I analyed before and also simulated@by@LTspice. If you have an interest pse refer to...
          Message 4 of 19 , Dec 4, 2012
          • 0 Attachment
            Hi Alan
            > Did you read this? http://groups.yahoo.com/group/softrock40/message/55570

            Yes, I knew.
            I analyed before and also simulated@by@LTspice.
            If you have an interest pse refer to...

            http://dl.dropbox.com/u/85347415/HAM/temp/PA_Bias%20Circuit.doc

            JA1TLH/Taka
          • Alan
            ... Subject: [softrock40] Re: To match or not to match... BS170s in your RXTX Sorry Taka, I am too dumb to understand. But finally I see. I need simple
            Message 5 of 19 , Dec 4, 2012
            • 0 Attachment
              ----- Original Message -----
              Subject: [softrock40] Re: To match or not to match... BS170s in your RXTX


              Sorry Taka,

              I am too dumb to understand.

              But finally I see. I need simple explanations without mathematics.
              Q4 is configured to pass a constant current through R41. It does this by controlling Q5.
              So Q5 source/gate voltage is set by Q4 so it will pass that constant current keeping Q4 base at ~0V7.
              Q5 gate voltage will vary according to the temperature of Q5 (in thermal contact with Q7/8) and is sent to Q7/8 with D3 dropping
              ~0V7 to compensate for Q4 base voltage.

              Simple, but not as simple as me.

              73 Alan G4ZFQ
            Your message has been successfully submitted and would be delivered to recipients shortly.