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Marshall JCM 2000, 1998

Discussion in 'Electronic Repair' started by N_Cook, Mar 10, 2011.

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  1. N_Cook

    N_Cook Guest

    Blown primary of the mains Tx, isolated removed from chassis, draws 1.2 amp
    at 20V variac "mains" and temp climbs 20 deg C in 4 minutes or so.
    Secondaries measure l27V, 16.3V and 2V so that side presumably ok.
    DC of primaries measure 1.2R and 2.2R, would they use 2 bifilar primary
    windings where stressed midpoint would show half way short and half measured
    ohms?. I will poke around in the winding/ try delaminating out of curiosity
    but
    stock fault/ batch fault ? Other than "marinating" in paint stripper , any
    tips on delaminating ?
    Are replacements available from Marshall ? or a grey market source UK ? or
    anyone use 2 or 3 separate Tx ? Googling Tx model
    Dagnall, TXMA 00061, D2105
    only shows up suspiciously low priced dollar quotes
     
  2. Meat Plow

    Meat Plow Guest

    http://www.mercurymagnetics.com/pages/mainframe.htm

    Should ship internationally.
     
  3. N_Cook

    N_Cook Guest


    Any ball-park idea of cost for a Marshall replacement ?
     
  4. N_Cook

    N_Cook Guest

    At least its the outer 120V primary at fault and a split bobbin so once the
    laminations are apart , easy to inspect. Tomorrow I will try a 125W iron
    concentrating on the central sliver of the first "E". Laid thin ptfe sheet
    heat insulation under the other 3 slivers. What will be the softening
    temperature of the lacquer and any guesses as to time of heat application at
    the exposed end only ? At least I can monitor the other end with a
    pyrommeter.
     
  5. N_Cook

    N_Cook Guest

  6. Phil Allison

    Phil Allison Guest

    "Nutcase Kook"

    ** The Dagnall brand trannies that are fitted to modern Marshalls are all
    made in India or Shi Lanka by starving children.

    The design is way under sized for the job and quality is non existent.

    Spares are cheap, IME.

    Shame the fucking amps are not.





    ...... Phil
     
  7. N_Cook

    N_Cook Guest

    Normal single filament winding. Normal failure mode , for slapdash wound Tx
    these days. Slipped turn at one end of a layer dropping into a lower layer,
    then presumably chaffing of lacquer to marginally spot weld. Not at all
    obvious "weld" point , about 80 turns from lead out of outer primary. 195
    turns in all of .75mm wire for one 120V primary. Not a problem here as 240 V
    use, but would be for this Tx used in USA . There is tape covering the inner
    primary but not extended at the leadout point of the inner primary so first
    turn of the outer primary directly crosses that point so a full short is
    very likely there with a bit of normal in service vibration/ chaffing. For
    240V use those 2 points are at near enough same mid-mains potential (2 tails
    to options bridging point on pcb)
    At least I now know how to delaminate the E/I iron laminations.
     
  8. Phil Allison

    Phil Allison Guest

    "Nutcase Kook"
    ** The turns wound on that transformer do no move or chaff - you wanker.

    Those Dagnall power transformers ( TMXA00061 etc) are made with low temp
    grade enamel coating the copper and the tranny is under sized for the job it
    has to do - not to mention working in a very high ambient temp from the heat
    of the output valves.

    As a result the windings run DAMN hot, the enamel gets soft and when two
    soft spots meet under pressure you can get a short.

    I have THREE dead ( internally shorted) examples of the exact same tranny
    sitting here right now.


    ..... Phil
     
  9. N_Cook

    N_Cook Guest

    Marshall replacement £46 , same duff construction as this one?
     
  10. Phil Allison

    Phil Allison Guest

    "N_Cook"
    ** Of course.

    Only way to fix the problem is to find someone willing to rewind the
    original transformer with high temp enamel wire - ie 180C rate instead of
    the 120C rated stuff used by Dagnall.

    Or you could fit a small fan blowing on the tranny....


    ...... Phil
     
  11. Phil Allison

    Phil Allison Guest

    "Gareth Magennis"
    "Phil Allison"
    ** Makes you as big a fucking halfwit as he is.

    ** HUH ???

    What sort of madness makes do you think the problem has a 13 year delay
    built in ??????

    That POS tranny can fail in the first few hours of use !!!

    Only has to overheat enough to soften the enamel on the wire - and overheat
    it surely will cos it is not correctly sized ( in terms of VA rating) for
    the job it has to do.



    ...... Phil
     
  12. Phil Allison

    Phil Allison Guest

    "Arfa Daily"


    ** Please come to Sydney - Arfa.

    Just buy a one way ticket, cos that is all you will need.

    Go straight to Circular Quay from Mascot airport and then into any pub with
    your stupid, whiny pommy voice and tell everyone there all your brilliant
    thoughts.

    The sharks in Sydney harbour will be picking your bones by nightfall.



    ...... Phil
     
  13. N_Cook

    N_Cook Guest

    What is the point of CE "compliance" testing etc if 2 layers of lacquer to
    resist 120V av . At one time, before CE marking, all these Tx tails had
    extra sleeving over them to avoid this problem.
     
  14. Phil Allison

    Phil Allison Guest

    "Gareth Magennis"

    ** So it is always " cold wet and miserable " INSIDE a venue in summer
    plus INSIDE a Marshall valve amp playing " Death Metal " riffs to hundreds
    of head bangers in the UK - is it ??

    God, what a fuckwit you are.



    ** The easy and engineering wise final solution is the re-wind I suggested.

    **** head.



    ..... Phil
     
  15. N_Cook

    N_Cook Guest

    For balance I got a quote from proper tx winders Majestic , just down the
    road
    http://www.transformers.uk.com/brochure.pdf
    for a one off , custom/semicustom build from scratch , to specified V & A of
    the 3 secondaries. Somewhere between 50 and 70 GBP plus VAT plus carriage,
    about 2 week turn around
     
  16. Phil Allison

    Phil Allison Guest

    "Nutcase Kook "

    ** That is a very reasonable price.

    But did you ask them to make a new tranny with the exact same stack size and
    through chassis design as the Dagnall ones ??

    Were they offering you a custom toroidal tranny by any chance??


    ...... Phil
     
  17. Phil Allison

    Phil Allison Guest

    "Gareth Magennis is an utter ASS "
    ** Go shove you stupid fucking database up you stupid fat arse !!

    Engineering facts are F A C T S !!

    You pathetic, pommy DUMBASS !!



    ..... Phil
     
  18. Phil Allison

    Phil Allison Guest

    "Gareth Magennis"


    ** Bullshit stats YOU INVENTED are not engineering facts !!

    YOU GOD ALMIGHTY KNOW NOTHING POMMY ****
     
  19. Or perhaps he'll get his head stomped on by an irate kangaroo...

    Disembowelment from a kick is more likely.

    Herbivores are more dangerous than carnivores.
     
  20. N_Cook

    N_Cook Guest

    Added a 12V 1.5 inch fan at the Tx. Using the unused heater tag for main
    mount of the fan to solder a solder tag then that bolted to the fan.
    Setting fan at 20 degrees to the horizontal and cutting and fitting a
    shroud from that red impregnated cardboard stuff to direct the flow into one
    side , up, over top and back out the other side between windings and bobbin.
    As secondary side gets hotter than primary , fan positioned mainly on that
    side
    Air flow checked using a joss stick. Perhaps next time using some DC from
    the amp rather than bridge rect and cap off the heater supply as light
    current drops in the diodes bring it down to less than 9V . Retained the
    template for the shroud for the next one of these to attend to.
     
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