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Re: Ensemble RXTX PA problem

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  • g8voip
    Hi Sid, Drawing 2.4A on transmit, I would expect the poor PA FETs to be merrily glowing! Wonder where all that current is going? How hot is the 2N2222A driver?
    Message 1 of 6 , Apr 29, 2011
      Hi Sid,

      Drawing 2.4A on transmit, I would expect the poor PA FETs to be merrily glowing!

      Wonder where all that current is going?

      How hot is the 2N2222A driver?

      On my v6.3 RXTX, after a 2 minute cycle of running WSPR at 1W, the PA heatsink is decidedly hot to touch. Not measured it, certainly not above the pain threshold of around 60 deg C, but starts to become a little uncomfortable, same goes for the driver.

      73, Bob G8VOI


      --- In softrock40@yahoogroups.com, Sid Boyce <sboyce@...> wrote:
      >
      > Did more tests with a dual tone sine and cosine.
      >
      > With sinewave audio input R25 - R28 hairpins 1.2V p-p.
      > 5.5V p-p at the antenna, 2V p-p at the 2N3866 collector.
      > Total current draw 1.47A.
      > I'd expect more amplification from the PA stage, that's just a gain of 2.
      >
      > 10.5V p-p Max at antenna socket with increasing audio levels and audio
      > is almost a square wave measured at R25 - R28.
      > Current draw on TX is 2.4A, heatsink is still cool to the touch.
      > 73 ... Sid.
      >
      > On 29/04/11 17:30, Sid Boyce wrote:
      > > On 29/04/11 16:36, Alan wrote:
      > > >
      > > > ----- Original Message -----
      > > > From: "Sid
      > > > Subject: [softrock40] Ensemble RXTX PA problem
      > > >
      > > > > I'm getting no output from the PA stage. I can send tones and get
      > > driver
      > > > > output around 3V p-p.
      > > >
      > > > Sid,
      > > >
      > > > Where, and how , do you measure this?
      > > > Can you measure anything on T3 secondaries?
      > > >
      > > Measured with a scope at the output of T3.
      > >
      > > > > I've rewound T3.
      > > > > R48 = 40.6mA
      > > > > R49 = 32.1mA
      > > >
      > > > Are these the static readings? Do they increase when driven? As the
      > > BS170s
      > > > stay cool it seems they are not taking current for some reason.
      > > > Does the Softrock draw substantially more current on TX?
      > >
      > > These are static readings with PTT on.
      > > Static current draw 22mA on RX and 110mA with PTT on which seems to be
      > > not far out of range with Robby's figures.
      > >
      > > Changed my meter, varying between 23.12mA and 23.6mA on RX and varying
      > > between 1113.4mA and 114.8mA.
      > >
      > > >
      > > > 73 Alan G4ZFQ
      > > >
      > > > > C - D = 2.62V
      > > > > R35 hairpin = 12.75V on TX 0V on RX.
      > > > > Bias at R46/R47 junction = 2.61V
      > > > > T4 Primary solid 13.04V on all legs and I've yet to remove the heatsink
      > > > > and check the voltage at the drains of the BS170's as I'm not feeling
      > > > > any warmth when I switch the PTT on for quite a long time.
      > > > >
      > > > > I'm beginning to suspect a problem with the BS170's.
      > > > > Would welcome suggestions before I go ahead and change them.
      > > >
      > > 73 ... Sid.
      > >
      > > --
      > > 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 ... 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
      >
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