1959hw Question - Revisions?

Discussion in 'Marshall Amps' started by cooljuk, Apr 1, 2019.

  1. ampmadscientist

    ampmadscientist Well-Known Member

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    One of the few significant changes I noticed was: addition of hum balance pot.
    This may or may not be inside your HW....but I think probably it is.
     
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  2. cooljuk

    cooljuk Active Member

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    Interesting. Though I may not mod it, at least for a while, I'll definitely take the chassis out and get some gut shots for record of the circuit, etc. I'll probably re-tube and bias it, anyway.
     
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  3. lespaul6

    lespaul6 Active Member

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    congrats OP.. its a great amp. And there isnt a thing wrong with those dagnall transformers. No one who is criticizing them actually knows what in hell they are talking about e.g. is it the steel used? if so, prove inferior steel? is it the winding method? prove specifically what is lacking? is it the insulation material? please provide evidence how this is sub par... they cant. Most important is the primary impedance- paper vs plastic is nonsense. Enjoy your amp!
     
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  4. ampmadscientist

    ampmadscientist Well-Known Member

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    If there is a hum balance pot in your amp, it's probably better to remove it and replace it with resistors.
    The hum balance pot explodes.
    When this happens, you will hear a lot of loud humming. (now you know why)

    The hum balance pot is replaced with 2X 100 ohm 1/2 watt resistors. This (so far) has solved the problems.

    [​IMG]

    No I wasn't kidding. The hum balance pot really does explode. I have seen this happen at least 4 times in 4 amps.
     
    Last edited: Apr 14, 2019
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  5. cooljuk

    cooljuk Active Member

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    That looks like a 1987x.

    You're saying the 1959HW can have a similar pot?
     
  6. Yamariv

    Yamariv Well-Known Member

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    Congrats James! Remember, Pics or it didn't happen though.. :fingersx:
     
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  7. cooljuk

    cooljuk Active Member

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    I was just waiting for a time to be available with it during daylight. :D

    I'll get some today, including gut shots.
     
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  8. cooljuk

    cooljuk Active Member

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    Opened it up to check and adjust the bias, today. I was sure to get some glorious gut shots...

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  9. K2JLX

    K2JLX Well-Known Member Gold Supporting Member

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    Gorgeous amp, and nice shooter on the bench, holstered.
     
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  10. Yamariv

    Yamariv Well-Known Member

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    Wow, she looks minty! Nice score James!
     
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  11. cooljuk

    cooljuk Active Member

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    Do you guys know if anyone has done a comparison demo of the 4 Ohm / 16 Ohm outputs through the same four speakers? ....because of the variable negative feedback in this circuit being tied to the impedance selector switch, I mean. I've messed with negative feedback on amps before but, at least to me, each type of amp seems to respond differently to changing it.
     
  12. cooljuk

    cooljuk Active Member

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    btw -
    In a strange turn of events, that seemed extremely shady at first but ended up working out, I got an extra set of Chinese G12M 75Hz speakers with that cab, in addition to the factory UK G12H 55Hz set.

    The Chinese ones don't sound awful. :shock:
     
  13. OdgeUK

    OdgeUK Member

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    1959HW looks like it using a split cathode setup, not shared.
     
  14. cooljuk

    cooljuk Active Member

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    It is. You can see the extra resistor cap on the input side of the board. At least mine is and so is the 1959HW schematic Marshall put out.
     
  15. cooljuk

    cooljuk Active Member

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    A two year old bump to remind me that, at one point, that in-house workbench was actually CLEAN!
    I can hardly turn around in that room, now.

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