PT wires not matching 100 watt MV Instructions

Discussion in 'Building the Classics' started by dinkyguitar, Feb 18, 2021.

  1. dinkyguitar

    dinkyguitar Active Member

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    Hi All,

    I'm starting to build my Valvestorm 100 watt MV using the Valvestorm instructions along with Mojotones PT:
    https://www.mojotone.com/amp-parts/...Style-Plexi-JCM800-100-Watt-Power-Transformer

    The instructions on page 6 have the input wires Orange(common), Red(120v), Blue(220v), Purple((240v) in the upper right hole.

    And the high voltage output wires Red, Red/Yellow, Red in the left hole.

    My PT has them reversed, but bias wires & heater wires are where they should be.

    What I don't understand is that Metro's PT schematics as well as mine have the input wires on the left & output wires on the right.

    Does the MetroAmp 1203-80-MS really have the 4 input wires on the right side?

    I could just hook up the wires as is....all the leads are long enough anyway.

    dinky
     
    Last edited: Feb 18, 2021
  2. Chris-in-LA

    Chris-in-LA Well-Known Member

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    As long as you follow the Mojotone colors you should be fine. I think my Mojotone 50 watt PT has the wires all coming out of one side. My 35watt Metro PT has all the power wires on one side and the wires for the heaters and rectifier on the other side. I don’t think it matters. And yes, you will have some long runs of wire.
     
  3. 2L man

    2L man Member

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    Measure resistances! They don't match the voltages but you see the pattern between them.

    On input coil 120 should come about middle between 0 and 240 and there is small resistance between 220 and 240

    On output a CT is between HV and if it has bias coil it is close the CT. Heaters are almost 0. Between coils it should come infinite.
     
    neikeel likes this.
  4. william vogel

    william vogel Well-Known Member

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    I suggest you call Phil or Arlyn at Heyboer and tell them the transformer number on the sticker. They will tell you exactly what you need to know. Changes are made and Mojotone doesn’t update their wire schematics.
     
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  5. Travis398

    Travis398 Well-Known Member

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    It doesn't matter what hole the wires go through, if they are long enough to reach they all get bundled together in the amp anyways.
     
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  6. dinkyguitar

    dinkyguitar Active Member

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    I measured the resistance using the lowest Ohm setting and this is what I got.

    According to the readings I got, the wire placement looks correct.

    PT Resistance.jpg
     
  7. 2L man

    2L man Member

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    Those values are logical! When 120V use takes more current it is good to wound it using thicker wire and its resistance is less than what comes from 120V to 240V. I forgot that when I wrote earlier. Other way to make usiversal transformer primary is to use two coils where they are used parallel for 120V and series for 230V. Sometimes there are two coils having 0-110-120. Using two primarys is more economical way to make transformer when it needs less copper VS. when one primary is used for 120V the wire for 230V is useless and when for 230V the wire in 120V section is unnecessarily thick.

    There your bias coil has proportionally more resistance than HV when it is wound using thinner wire and it delivers less current. If bias is taken from same secondary the HV is then its resistance has almost same proportion because there must be same thickness wire when all the current HV delivers runs thru it. Some difference there often comes is when wounds which are done "to the bottom" needs less wire when coil diameter is smaller...

    ...This can be confusing when Push Pull Output Transformer resistances are measured when PP primary halfs can be different. There is "bifilar" way to wound PP OPT where both primarys are wound same time using two wires but it increase stray capacitance between them and decrease high frequency efficiency which for guitar amp should come high enough but not for HiFi. Best way to wound OPT is to use "dividers" between each coils which stack coils next to each other.
     
    Last edited: Feb 20, 2021
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  8. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    I prefer the AC Mains (input wires) in the left hole so I can stuff them down into the left side corner of the chassis.
     
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