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HELP please OTL tube headphone amp (again)

Discussion in 'Audio' started by Ian Mason, Jan 10, 2018.

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  1. Ian Mason

    Ian Mason

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    0
    Dec 24, 2017
    Hi again all, thanks for all of your input on the amp last time, I have now finished the build having followed the schematic to the letter as it were but unfortunately it is not working and I just
    wondered if anyone could spot any glaring mistakes from the ridiculous amount of photos that I have uploaded, I am a bit of a novice and I do realise that this project is
    a bit beyond my capabilities but I have started and I'm now eager to hear the results, better still would there be anyone that is close to London, Uk, that could take a look
    for me, happy to buy you a pint or two, the problem I have is that I don't really know where to start with the diagnosis and I'm not comfortable working with these kind of
    voltages until I further my electronics knowledge, all replies are very much appreciated and thanks in advance.
    Thanks Ian
    PS sorry about all of the photos but I thought it best to show everything, hope to hear what you think Duke
     

    Attached Files:

  2. kellys_eye

    kellys_eye

    4,277
    1,146
    Jun 25, 2010
    can you put the tube pin numbering on the schematic?
     
  3. Ian Mason

    Ian Mason

    32
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    Dec 24, 2017
  4. Ian Mason

    Ian Mason

    32
    0
    Dec 24, 2017
    On the photos 7 and 8 are the valve pins that have the 6.3v cables in them, then 1 is to the left of the 8 or right next to the small groove of the middle hole.
     
  5. Ian Mason

    Ian Mason

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    Dec 24, 2017
    The 27 Kohm resistor is on the 250v winding between the two 47uf/ 400v
     
  6. kellys_eye

    kellys_eye

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    1,146
    Jun 25, 2010
    Darn.... this is difficult to assess with too many pictures and not enough notification on the schematic (i.e. tube pin numbering).
     
  7. Ian Mason

    Ian Mason

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    Dec 24, 2017
    Are you referring to the two yellow capacitors
     
  8. kellys_eye

    kellys_eye

    4,277
    1,146
    Jun 25, 2010
    Yes, the yellow capacitor. Pin 5 to pin 5 - both are anodes according to the device datasheet. Where does it show such a connection for a capacitor?
     
  9. Ian Mason

    Ian Mason

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    0
    Dec 24, 2017
    Right in the middle of the two tubes on the schematic, these are the 0.47uf/ 630v, one from pin 2 of the 6sn7 to pin 1 of the 6080 and the other is from pin 5 of the 6sn7 to pin 4 of the 6080
     
  10. kellys_eye

    kellys_eye

    4,277
    1,146
    Jun 25, 2010
    Yes, my bad. Can't count! I'd have to draw the whole construction procedure out to follow your build. Have you done simple connectivity tests between the tube base connections? Tubes removed of course?
     
  11. Ian Mason

    Ian Mason

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    0
    Dec 24, 2017
    To be honest, I'm a complete novice and just don't know where to start or indeed go from here. Thanks for looking into it.
     
  12. Ian Mason

    Ian Mason

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    0
    Dec 24, 2017
    I would tag a photo for you of the valve numbering but the photos with tags don't upload for some reason
     
  13. duke37

    duke37

    5,301
    740
    Jan 9, 2011
    The valve base connections in both cases are
    gak gak hh
    international octal IO26 and IO145, I do not know why they were given different numbers.

    Disconnect the HT supplies at the rectifiers.
    Measure the voltage at p7 to p8 on both valve bases. It should be 6.3V or a bit above.
    Plug in the valves and look carefully to see if the filaments are hot.

    6080
    Make sure that a resistance is connected p1 to chassis and p2 to chassis
    Connect up the 150V supply and check that it is connected to p2 and p5 (anodes)
    Make sure there are resistors cathodes to chassis P3 and p6.
    Measure the voltages at the cathodes, it should be about 30V.

    Let us know the results so far.
     
  14. shrtrnd

    shrtrnd

    3,701
    462
    Jan 15, 2010
    This probably going to turn into a very long thread with people submitting helpful suggestions. My initial input is, congratulations on (almost0 completing this project on your own. People like you who chose to do their own work are rare these days. My secondary input, is that you probably have something(s) wired incorrectly, even though you believe you followed the schematics to the letter. You'll get plenty of input from other here. But my input is to start going through your assembly device by device again, looking for wiring errors (even though you won't want to). ASSUME NOTHING, VERIFY each connections even if it seems insignificant during the hunt.
    Good luck.
     
  15. Ian Mason

    Ian Mason

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    Dec 24, 2017
    Thank you very much, it means a lot, my problem is that I should have looked into understanding the circuit before I started the build, I realise that it is a dangerous thing to deal with these voltages and that is why I am not able to run the tests needed, I will do as you say and check everything, thanks again.
     
  16. Ian Mason

    Ian Mason

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    Dec 24, 2017
    Please forgive my ignorance but can I put this in novice terms, when I disconnect the positive on the two bridge rectifiers does this then make the circuit safe for me to check the p7 and p8 valve pins, I have already put power through the circuit but the valves didn't glow at all (I'm presuming that some of the capacitors will now be holding a charge)
    When I connect the 150v supply back, I'm presuming that this is not now safe and that extra care is needed.
    The resistors (320 ohm) are not currently coming from P3 and P6, they are connected to the 2x 1000uf/ 300v capacitors and then to ground (photo attached), the same 1000uf/ 300v are connected to wire that goes to P3 and P6, should I move the resistors to P3 and P6.
    Thanks Ian
     

    Attached Files:

  17. kellys_eye

    kellys_eye

    4,277
    1,146
    Jun 25, 2010
    I reckon your problems stem from not having the component designations written down, C1, C2, R1 R2 etc even the tube socket pins aren't numbered! Do you have a drawing of the layout of your capacitors even?
     
  18. Ian Mason

    Ian Mason

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    Dec 24, 2017
    The schematic is the only thing that I have.
     
  19. 73's de Edd

    73's de Edd

    2,805
    1,176
    Aug 21, 2015
    Sir Ian Mason . . .

    I don't think that I ever saw that you ever performed a good and proper job on connecting up the center of the chassis filament connections.

    Your very first photo confirms to me that you have properly identified pins numbers 7 and 8.

    The filament connections on the tube the farthermost from the power transformer barely meet specs.

    The closest tubes socket filament pins have reddish brown enameled wire not soldered to.
    The wire ends coming from the power transformer need to be laboriously totally scraped free of all of the enameled coating on both wires until bare copper is seen. No final enameled coating presence permissible.
    Then you rosin flux coat the bare copper and then tin the wire ends until they look chrome plated with solder.
    Run the ends of the just tinned transformer wire ends into the socket pin holes. Reflow solder the pins. Prep the jumper wires to the other tube in the same manner. Install them between the tubes.
    see if you have lit up tubes this time.

    ILLUSTRATION:

    The YELLOW circled area may meet minimum specs.
    The RED area connectivity surely must be failing due to the wire still having its enamel insulative coating STILL on it. PLUS no solder.

    upload_2018-1-10_20-26-44.png


    73's de Edd
     
    Last edited by a moderator: Jan 11, 2018
  20. Ian Mason

    Ian Mason

    32
    0
    Dec 24, 2017
    Thank you, that seems to be what everyone thinks, I will remove them and start again after cleaning all of the enamel off of the wire, once again, thanks very much for your input.
     
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