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    rebuilding MkIV - problem

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    MarcVBelgium

    Posts : 83
    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    rebuilding MkIV - problem

    Post by MarcVBelgium on Sun Jul 13, 2014 11:58 am

    Hello everyone,

    It seems that I have a problem.. I'm rebuilding a set of MkIV mono's. When I dismantled the old ones,
    I did not mark the connections of the A-470 output transformers except for the one to the quad cap (#2)..
    It seems age has rendered the color of the leads into green/green (should be green/blue) and green/yellow
    (should be one green/yellow and one blue/yellow). They looked the same, so I thought marking was not needed.

    I should have read the manual in detail before...(sigh!) (I did mark the power transformer leads..)

    Guessing is not what I like to do....(what would happen if I connect them the wrong way?)

    Is there a way to "refresh" the faded colors, so that I could at least make an "educated guess"?

    Can anybody help?

    Thanks


    DynakitParts
    Admin

    Posts : 183
    Join date : 2008-11-30

    What are the color of these leads?

    Post by DynakitParts on Sun Jul 13, 2014 12:25 pm

    Hi,
    The exposed transformer cloth lead colors tend to fade over time. The leads within the end bell covers may have retained their original colors. Just remove the covers to confirm this.

    Kevin @ Dynakit

    MarcVBelgium

    Posts : 83
    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    Rebuilding MkIV - problem

    Post by MarcVBelgium on Sun Jul 13, 2014 12:40 pm

    Thanks, Kevin.

    I will check this and give some feedback. I hope it works out.. :-/

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: rebuilding MkIV - problem

    Post by Bob Latino on Sun Jul 13, 2014 9:46 pm

    Hi Marc,

    The wires on the Mark IV output transformer primary should be.

    RED
    BLUE
    BLUE/WHITE
    GREEN
    GREEN/WHITE

    Whay Kevin has said is quite true .. Underneath the bells the wire will change color very little and you should be able to see the true colors of the wires. Another cross check is (with the transformer outside of the amp and the wires free) measure the resistance from the RED wire to the BLUE/WHITE and the GREEN/WHITE wires. The resistance (probably 150 ohms or less) will be lower on the RED to GREEN/WHITE and higher on the RED to BLUE/WHITE. Similarly, the RED to GREEN resistance will be lower than the RED to BLUE resistance.

    Another thing that you can check on the Mark IV is the slight length difference in the wires. The GREEN and GREEN/WHITES should be just a little longer than the BLUE and BLUE/WHITES.

    The ironic thing is that when Dynaco had those transformers with the cloth leads made, they probably never figured that 50 to 60 years later the true colors on the cloth would fade and the people rebuilding these amps would have trouble seeing the true colors on the faded cloth.

    Bob

    MarcVBelgium

    Posts : 83
    Join date : 2013-12-06
    Age : 63
    Location : Antwerp, BELGIUM

    rebuilding MkIV - problem

    Post by MarcVBelgium on Mon Jul 14, 2014 4:59 am

    Kevin, Bob,

    Thanks a million times. After dismantling putting some powerfull halogen light
    on the wires, I could notice the differences, although very faint. Measuring the
    resistance between red and blue/green confirmed my findings.
    Marked the "blue" leads with blue crimping tape so this remains obvious for the next 25 years or so...
    Thanks!

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