Harvard 5F10 Build

Discussion in 'Shock Brother's DIY Amps' started by mjcyates, Nov 14, 2018.

  1. mjcyates

    mjcyates Tele-Meister

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    so quick update, I swapped the 1k resistor with the 10k resistor and I now have pleasant guitar sounds coming from the amp. I still need to do some cleanup. When I get that done I will re-check voltages and post back.
     
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  2. mjcyates

    mjcyates Tele-Meister

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    voltage on the Power Tube grids is now -40v
     
  3. mjcyates

    mjcyates Tele-Meister

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    I doubled up the 33k resistors to get 16.5k and now I can get the Power Tube grids down to -28v, currently have them at -30v
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    What is your B+ voltage now?
     
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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  6. mjcyates

    mjcyates Tele-Meister

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    This amp is driving me crazy, all of the voltages are worse now except for the Power Tube grids which appear to be where they should be.

    Heaters - 10.8 AC
    B+1 - 598 DC
    B+2 - 542 DC
    B+3 - 428 DC

    Bias Tap 89 AC in, -38 DC out

    V1 - 6AT6
    1 - 0
    2 - 2
    3 - Fil
    4 - Fil
    5 - NA
    6 - NA
    7 - 237

    V2 - 12AX7
    1 - 264
    2 - 0
    3 - 2
    4 - Fil
    5 - Fil
    6 - 333
    7 - 5
    8 - 82
    9 - Fil

    V3 - 6V6
    1 - 0
    2 - Fil
    3 - 586
    4 - 541
    5 - -31
    6 - -31
    7 - Fil
    8 - 0

    V4 - 6V6
    1 - 0
    2 - Fil
    3 - 587
    4 - 541
    5 - -31
    6 - -31
    7 - Fil
    8 - 0

    5Y3
    1 - NA
    2 - 8.7 AC
    3 - NA
    4 - 582 AC
    5 - NA
    6 - 582AC
    7 - NA
    8 - 600 DC

    Everything is functioning properly with the exception of the high voltage and a hum (volume dependent). Could this Power Transformer be bad?
     
  7. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I wouldn't turn it on again until someone has a viable suggestion. You're a 200v-300v higher than you should be.

    Maybe some new pictures and more close ups since you've been back in there a couple times?
     
  8. D'tar

    D'tar Tele-Afflicted

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    Looking at hammond 290cax you have multiple voltage options. Can you verify and explain how you have it wired?

    Check your meter and put in a fresh battery if you have any doubt

    If you need to take quick readings I would have this on the current limiter probably without tubes also. you can work with it until you get your heater voltage figured out. Hopefully all else will fall into line then.
     
  9. D'tar

    D'tar Tele-Afflicted

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    Looking back it seems you changed PT from 290cax in your picture to a 290bx?
     
  10. mjcyates

    mjcyates Tele-Meister

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    Yes PT is 290BX
     
  11. Lynxtrap

    Lynxtrap Tele-Holic

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    A

    Also with the red secondary wires going to the rectifier, grounded CT, you should be
    putting 660V (330-0-330) on the 5Y3 plates.
    That is then drawn down by 60V by the tube as should be, landing at 600V. AFAI understand.

    Would the be a way of utilizing only half the seconatry winding?
     
  12. D'tar

    D'tar Tele-Afflicted

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    Make sure your terminal strip tabs that your centertaps are on are actually grounded. Those strips are usually only grounded at the tab that boltas down and you would need to wire any other grounds to those tabs with jumpers.
     
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  13. mjcyates

    mjcyates Tele-Meister

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    Yeah I already discovered and fixed that problem:)
     
  14. mjcyates

    mjcyates Tele-Meister

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    So good news and frustrating news at the same time. None of this was making any sense so I decided to go buy a new multi-meter just to make sure that wasn't the problem and apparently it was. I just re-measured everything with the new meter and the numbers are much more in line.

    Heaters - 6.7 AC
    B+1 - 374 DC
    B+2 - 334 DC
    B+3 - 268 DC

    V1 - 6AT6
    1 - 0 DC
    2 - 1.7 DC
    3 - Fil 6.68 AC
    4 - Fil 6.68 AC
    5 - NA
    6 - NA
    7 - 156 DC

    V2 - 12AX7
    1 - 175 DC
    2 - 0 DC
    3 - 1.37 DC
    4 - Fil 6.68 AC
    5 - Fil 6.68 AC
    6 - 217 DC
    7 - 18 DC
    8 - 52 DC
    9 - Fil 6.68 AC

    V3 - 6V6
    1 - 0 DC
    2 - Fil 6.68 AC
    3 - 368 DC
    4 - 334 DC
    5 - -22 DC
    6 - -22 DC
    7 - Fil 6.68 AC
    8 - 0 DC

    V4 - 6V6
    1 - 0 DC
    2 - Fil 6.68 AC
    3 - 368 DC
    4 - 334 DC
    5 - -22 DC
    6 - -22 DC
    7 - Fil 6.68 AC
    8 - 0 DC

    5Y3
    1 - NA
    2 - 5.3 AC
    3 - NA
    4 - 351 AC
    5 - NA
    6 - 351 AC
    7 - NA
    8 - 373 DC
     
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  15. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Congratulations! I don't know about all the numbers off the top of my head, but 370v B+ is where I kept mine for a long time, it was 70% on Rob's calculator. Turns out I like it better colder in the upper 50's% now, but personal preference.



    Sent from my XT1585 using Tapatalk
     
  16. King Fan

    King Fan Friend of Leo's Ad Free Member

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    So it was just a fluke. Er, I mean, wasn’t a Fluke? :)


    Sent from my iPad using Tapatalk
     
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  17. mjcyates

    mjcyates Tele-Meister

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    Exactly, Craftsman piece of crap
     
  18. D'tar

    D'tar Tele-Afflicted

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    Ahhh... Those numbers are much better! Sigh of relief, right!!!

    I always check an AC outlet.. I can count on approx 122vac, and a regulated 12vdc power supply.

    Happy new meter day!
    And New healthy Harvard Day!!!
     
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  19. mjcyates

    mjcyates Tele-Meister

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    Thanks, the amp sounds really good, just need to try to reduce some hum.
     
  20. Nickfl

    Nickfl Tele-Afflicted

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    Just FYI, that's not how it works. when your rectifying the voltage of a center tapped transformer with a full wave rectifier it's the voltage from one end to the center tap that matters not the voltage across the whole secondary. So 330ac into the 5y3, x1.4 would give you approximate rectified dc with a solid state rectifier of about 460. Then subtract approximately 60v for a 5y3, so an estimated B+ of 400v. The OPs measured voltage is 25v lower than that, probably because the 330v Hammond is rating it for is either unloaded or with a lower current draw that what the OP's amp is running at.
     
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