Marshall Minor

Discussion in 'Building the Classics' started by Timbo, Sep 4, 2018.

  1. Timbo

    Timbo Member

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    Hi guys, I thought I'd have a bash at one of these....
    I was able to get hold of a cheap power transformer for $4.
    Not your usual. PT is 35v-0-35v@2.5A and doesn't have a heater supply, so another PT will do the heater supply and maybe a relay supply.
    A quadrupler circuit will be used to get the desired HT of around 380v loaded.
    I have used this PT in a JTM60 build and it works well.
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    A recycled chassis so there are a few extra unused holes.
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    I'm getting 412v unloaded.
     
    Geeze, jmp45 and ampmadscientist like this.
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Quadrupler?
    That is cavalier - wild child ! :applause: Is this a guitar amp, or a TV set? :lol:
     
  3. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    I love it! Some real hands-on engineering!
    Good luck!
     
  4. Timbo

    Timbo Member

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    Hi guys, A couple of progress pics.
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    Just waiting on a couple of components and we're good to go.
     
    neikeel, CraigP, jmp45 and 1 other person like this.
  5. ampmadscientist

    ampmadscientist Well-Known Member

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    That is cool in the old style p to p.
     
  6. Timbo

    Timbo Member

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    Hi guys, No problems on start up.
    Haven't had a chance to crank just yet but does sound very marshally.
    [​IMG]
    Very happy with the voltages from the MM2026 and think some 6L6s would be a treat.
    This datasheet
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    Shows some similar voltages and proposed power output.
    But when I use the bias calculator https://robrobinette.com/Tube_Bias_Calculator.htm
    The KT88s are not running at max plate dissipation, which I thought that cathode bias was all about.

    I need some educating.
     
  7. Timbo

    Timbo Member

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    Hi guys, All good, power tubes biased to correct plate dissipation.
    I'm not much of a guitarist but it's got awesome Marshall grind and loud, VERY LOUD:applause:
     
    tschrama likes this.
  8. Timbo

    Timbo Member

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    Hi guys, Finally got around to making a cab for this one....
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    Just got to work on a faceplate.
     
    tce63 likes this.
  9. Timbo

    Timbo Member

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    A couple of extra pics..
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  10. jensvonbustenskjol

    jensvonbustenskjol Active Member

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    Congratulations :) very nice built!! I bet it sound amazing work those tubes, and that pure layout. Les is more :)

    I bet it has sweet headrom :)
     
    tce63 likes this.
  11. Exojam

    Exojam Active Member

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    Timbo,

    A couple of questions for you.

    Did you design that yourself or did you find it on the web? Either way it a cool as hell.

    And since I have know idea, what the heck is a quadrupler?

    It looks like one of this projects you do when you go through your first electronics courses (not the final build).

    I love it and glad it came out to your statisfaction.
     
  12. Timbo

    Timbo Member

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    Thanks guys.
    Exojam, I live in Australia and shipping cost and the Aussie $ make buying transformers expensive.
    The local guys here are always looking for a cheaper alternative.
    Some local produce here. http://www.ozvalveamps.org/
     

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