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RM Station 550

Discussion in 'Amplifiers' started by redlght, Dec 17, 2016.

  1. redlght

    redlght Active Member

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    RF final 35.19
    Rf final base No volts
    all legs of of TR9 no volts amp power on in standby
    supply voltage 13.21 keyed and unkeyd
    base tr8 unkeyd .752 volts keyed no volts
    R29 35 volts on standby switch side no volts on c34.... R29 shows 1 ohm
    C34 shows ground on both sides


     
    #31 redlght, Dec 18, 2016
    Last edited: Dec 18, 2016

  2. bob85

    bob85 Supporting Member

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    You wont have bias voltage in standby.

    Jumpering tr3 will confirm the maximum no drive bias voltage when turned hard on. A situation that never happens in the stock amp but it can when the bias is fixed.

    It won't reveal the cause of the class C sounding ssb in stock 550's.
    That happens when tr3 is only partially turned on with rf drive.

    Theres too much voltage on the base of tr8.
    Its a stupid design relying on the base emitter junction of tr8 to be the only load for r29. Made even worse by your high supply voltage.

    The resistor i added connects from the base of tr8 to ground forming a variable potential divider with r29 so you can set the bias turn on point

    10w max drive FM/SSB 2.5w deadkey or less Am.

    Believe RM at your own peril
     
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  3. sp5it

    sp5it Master of puppets

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    [​IMG]
    S3 need to be closed. Not open.
    Red line is how bias voltage goes.
    What is the voltage on TR9 collector?
    Mike
     
  4. redlght

    redlght Active Member

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    S3 was closed and what can i do about the high supply voltage? and i am getting no voltage out of R 29
     
    #34 redlght, Dec 18, 2016
    Last edited: Dec 18, 2016
  5. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    This all should be done with out RF Exciter(Radio) attached or keying in dead key. The collector of TR3 grounded or the Cathode of D-18 to ground you should hear Relay #2 click in and out.

    RF final 35.19 (Good)
    Rf final base No volts (Good if unkeyed)
    all legs of of TR9 no volts amp power on in standby(Good)
    supply voltage 13.21 keyed and unkeyd (Good)
    base tr8 unkeyd .752 volts keyed no volts (What Position Stand by?)
    R29 23 volts on standby switch side no volts on c34.... R29 shows 1 ohm.(Good)

    When relay #2 is keyed and STBY switch is connected the fans should turn on, and DC voltage should be applied to the center tap of T3. In turn the base voltage TR7 and TR8 should be present.
     
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  6. redlght

    redlght Active Member

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    stanby on and as far as R29 get no volts out of it on the c34 side
     
  7. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Might be a burned trace or bad solder joint or even a solder short. If the resistor reads one ohm it should conduct.
     
  8. sp5it

    sp5it Master of puppets

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    Check TR8 and TR9. No voltage on c34 side means it is shorted to ground.
    Can be shorted by c34 or tr8
    Mike
     
  9. redlght

    redlght Active Member

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    ripping it apart now
     
  10. redlght

    redlght Active Member

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    R29 is open
     
  11. sp5it

    sp5it Master of puppets

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    Replace it :)
     
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  12. redlght

    redlght Active Member

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    it is on order be a few days before i get back with an update
     
  13. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Bob85 said:
    Jumpering tr3 will confirm the maximum no drive bias voltage when turned hard on. A situation that never happens in the stock amp but it can when the bias is fixed.
    Tallman said: This is incorrect. this area of the circuit is either on or off. No hard, no soft. just on or off.

    It won't reveal the cause of the class C sounding ssb in stock 550's.
    That happens when tr3 is only partially turned on with rf drive.
    Tallman said:This exactly how the bias is set by jumping the collector of TR3 to ground and then putting a pot in place of R31 and measuring the current of the final transistor and adjusting it till you get the preferred Quiescent for the transistor. Must be matched pair.

    Theres too much voltage on the base of tr8.
    Its a stupid design relying on the base emitter junction of tr8 to be the only load for r29. Made even worse by your high supply voltage.
    Tallman said:The supply voltage is just fine. There could not be too much voltage on the base of TR8 since R29 was an open circuit. This is a very common circuit used all over the place and not too bad of a design.

    I do have an email from RM Italy detailing the bias adjustment.
     
    #43 Tallman, Dec 18, 2016
    Last edited: Dec 19, 2016
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  14. redlght

    redlght Active Member

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    Any bias or other info is always appreciated.
     
  15. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Replace R31 with a 5 Kohm pot and use an ammeter that can measure the low milliamps needed to get the quiescent current set to the power transistors. Which will get you to the AB class operation instead a double class c. If you need more help just let me know.
     

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    #45 Tallman, Dec 18, 2016
    Last edited: Dec 19, 2016
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