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PR build troubles, any Ideas?

Discussion in 'Shock Brother's DIY Amps' started by Mark the Moose, Jan 3, 2020.

  1. Mark the Moose

    Mark the Moose Tele-Holic

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    Building the Weber 6a14hp, a 6l6 Princeton Reverb. All tubes have a nice glow, no red plating. No sound, low B+.

    B+1 is 262, B+2 is 258 and B+3 is 230.

    All voltage measure measurements at V1 also seem to be about 2/3 what they ought to be.

    My only guess is that I used the wrong PT lead to the AC input. It has a 120v input and a 125 v input. I used the 125 thinking that would be safer and only make a tiny difference on the back end. Could that be it?

    the OT leads to the 6l6 tubes are both 262v as well.

    ideas?
     
  2. FenderLover

    FenderLover Poster Extraordinaire

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    I wouldn't worry about the input AC leads just yet. You don't have sound, so there is something different going on for sure and it could be literally anything. Can you post the plate and cathode voltages of the tubes, and show a few pics of the wiring, particularly the output stage? Is your bias set?
     
    Last edited: Jan 3, 2020
    Mark the Moose and Snfoilhat like this.
  3. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Double check the ground connection on your cap can.
     
  4. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    AC voltages right at the recitifier may be helpful here as well, since everything is low across the board.
     
  5. Mark the Moose

    Mark the Moose Tele-Holic

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    Double checked everything at the cap can and I went ahead and changed the PT feed from 125v to 120v. Here are my voltage measurements:

    B+1 279v
    B+2 273v
    B+3 244v
    B+4 180v

    Everything seems to come in around 2/3 what I expect to see according to the layout below.

    If I'm measuring correctly, the red wires from the PT to the rectifier are reading:
    Rectifier pin 4 332v AC & 6 60v AC.

    (I measured the red probe on the wire and the black probe on the neutral AC wire, let me know if that should be done differently.)

    V6
    3 279v
    4 275v

    V5
    3 279v
    4 275v

    V4
    1 171v
    3 1.49v
    6 142v
    8 38v

    V3
    1 125v
    3 .82v
    6 125v
    8 .86v

    V2
    1 272v
    3 5v
    8 5v

    V1
    1 129v
    3 .76v
    6 123v

    Here is RobRob's signal flow layout with voltages.
    AA1164_Princeton_Reverb_Signal_Flow_Layout.png
     
  6. Mark the Moose

    Mark the Moose Tele-Holic

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    The low measurement at the rectifier pin 6 makes me question whether the PT is bad. Is there a way to test the PT?
     
  7. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    If the amp is grounded in a standard American outlet, measure with black on ground, not neutral.

    Yes, those numbers seem odd and could indicate a bad PT, but test again with black on ground and let us know.
     
  8. schmee

    schmee Doctor of Teleocity Silver Supporter

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    No sound at all?
    Double check all the wiring. I have this trouble almost every time I start up a build. One thing either wrong or a wire missing. Especially those under board wires.
    Don't worry about voltages being off 20% or so for now.
     
  9. Mark the Moose

    Mark the Moose Tele-Holic

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    Then I get 213v and 172v.
     
  10. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Alrighty, let's do this.

    Pull the rectifier tube.

    Measure the AC of the red wires right on the rectifier socket. What do you get there? Is that your 213 and 172?
     
  11. Mark the Moose

    Mark the Moose Tele-Holic

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    Should I start with all of the tubes pulled, or just pull the rectifier?
     
  12. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    We only care about what's coming out of the transformer at this point, so we just need the rectifier pulled for this test, although pulling more won't hurt anything.

    Could you also let us know the specific power transformer you're using?
     
  13. Mark the Moose

    Mark the Moose Tele-Holic

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    With the rectifier pulled I get 419v and 320v.

    Tranny is:

    Weber W025130:
    w025130sch.JPG
     
  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Seems odd - got some pictures of the wiring around the rectifier tube socket? According to that diagram I'd like to see somewhere around 340V on each red wire.

    Is the red/yel wire grounded?
     
  15. Mark the Moose

    Mark the Moose Tele-Holic

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    That question causes me to wonder if I misread the layout...

    I used the "optional resistors" and taped off both the green/yellow AND the red/yellow. But looking again I think perhaps the red/yellow needs to be grounded in either case.

    6a14hp_layout-2.jpg
     
  16. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    If you have the option, always go with the real center tap instead of the resistors. I'd remove the resistors and ground the green/yel and red/yel wires. Then see where you're at :D
     
  17. Junior Little

    Junior Little Tele-Meister

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    Yep, I'm with @corliss1 on this one:
    ground that red/yellow wire.
     
  18. Mark the Moose

    Mark the Moose Tele-Holic

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    Boom! That was it. Dead quiet and sounds awesome! Thanks so much for your help, if you find yourself in CO I owe you a cold one.
     
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  19. mjcyates

    mjcyates Tele-Meister

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    Another "Happily Ever After"! Glad you got it figured out.
     
  20. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Yay!
     
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