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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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    The 1 ohm smoked a few seconds after i powered amp up
    With C34 out of line Tr9's collector shows ground


     
    #61 redlght, Dec 23, 2016
    Last edited: Dec 23, 2016

  2. redlght

    redlght Active Member

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    On the schematic it shows TR9 as BD241....the transistor i took out says BD179
    That ones a 20 dollar part... This has been more of a learning experience than fixing an amp it has nickled and dimed me past the point of its worth lol
     
    #62 redlght, Dec 23, 2016
    Last edited: Dec 23, 2016
  3. redlght

    redlght Active Member

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    This reminds me of some of the cars i worked on in the 70's and 80's that the same car had 4 different flywheels 3 different sets of crank pulleys ect was no standardizing between them just what ever left over parts they had to use at the time.

    Total to date of parts replaced:
    TR10
    IC2
    IC1
    TR7
    R29 x 2
    F1 F2 and guards
    About to be TR9
     
  4. bob85

    bob85 Supporting Member

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    Bd179 is what older RM & zetagi amps used.
    last time i bought some they were a 2 dollar part.
    If the 1ohm is open tr9 collector is grounded through resistor & tr8.
     
  5. redlght

    redlght Active Member

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    I put a new 1 ohm in that's when it smoked
     
  6. redlght

    redlght Active Member

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    Got a schematic laying around for that old version? I have been running using a schematic for a newer style and it is not working well for me.
    Any chance on using an nte152 in it's place with lead changes?


    In all these years you would think i would learn when to toss in the towel be it as it may. I have not. lol
     
    #66 redlght, Dec 23, 2016
    Last edited: Dec 23, 2016
  7. redlght

    redlght Active Member

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    TR9 in the newer amp can use a NTE152 the version i have uses a BD179 or NTE182
    But they have different current ratings but seems both versions use the same parts as each other all but TR9. maybe remote mount a NTE152 in it's place? Did they find they could use a part with less current handling or did they change something to lower it in the new versions?
     
    #67 redlght, Dec 23, 2016
    Last edited: Dec 23, 2016
  8. bob85

    bob85 Supporting Member

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    I probably have the schematic for early versions on my old pc but i can't get to it right now. I moved house & most of my stuff is at the old place.

    The later amps use a larger higher
    rated pass transistor,
    Just about anything comparable to the bd179 or higher rated with a similar hfe will work with the standard parts.

    179's are worth 2 dollars max or buy something better.

    If you remote the transistor make sure you don't get rf on the wires.
     
  9. redlght

    redlght Active Member

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    I used a nte152 seems to work now but it is not heat sinked yet. I can not find bd179's for under 20 dollars US. Also if you run acrossed The schematic I would like a copy. Thanks


    It no longer has that tunneling on the scope trace so that is a plus.
     
    #69 redlght, Dec 23, 2016
    Last edited: Dec 23, 2016
  10. bob85

    bob85 Supporting Member

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    It needs to be heatsinked. The pass transistor dissipates a fair amount of heat at high drive.
    As the transistor gets hot conduction increases & bias voltage increases for the same base emitter voltage.

    That's not what we want.
    Voltage needs to go down as the amp heats up to maintain the same idle current.
    Smoking 1ohm within seconds of powering up sounds like you forgot the mica insulator under the bd179.
     
  11. redlght

    redlght Active Member

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    It was shorted out. it tested as a 33ohm resistor on 2 of the legs on my component tester
     
  12. redlght

    redlght Active Member

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    Trace with amp off and on
     

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  13. redlght

    redlght Active Member

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  14. redlght

    redlght Active Member

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  15. redlght

    redlght Active Member

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    Found the BD179's for 15 shipped for 2 of them at Cricklewood Electronics Ltd I will try those when they come in
     

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