Replacing a rectifier on a Marshall DLS401 amp

Discussion in 'The Projects Forum' started by Steallearning, Dec 29, 2014.

  1. Steallearning

    Thread Starter New Member

    Dec 29, 2014
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    The Marshall DLS 401 amp is notorious for having a overheating problem with it's bridge rectifier and I was wondering if replacing the original rectifier with a larger one could damage the amp in the long run.
    Here's a link to a page where this has been done: http://pbenco.wordpress.com/dsl401-repair/
    My question is, would I be better off replacing the rectifier with one that has the original specs?
    Maybe glue on a heat sink?
     
  2. Kermit2

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    just adding a small fan close to it would probably work too.
     
  3. #12

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    Nov 30, 2010
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    When dealing with vacuum tube voltages, the differences between one solid state rectifier and another are pretty much zero. What? It produces a tenth of a volt more? Compared to 400 volts on the tubes? Means nothing.

    If you were talking about a solid state rectifier compared to a 5Y3, that is trouble coming your way with nearly 80 volts of difference.

    All that's left is heat. Give it longer legs to get it up off the board, attach a heat sink, use a rectifier in a larger case, all the same. Getting rid of heat is mostly physical.

    Adding a fan, any fan, can make a world of difference, even a tiny video card fan. Problem is, you have to modify the case to do that. Underwriters Laboratories would send a S.W.A.T team after me if I told you to make a hole in the sheet metal.
     
  4. Steallearning

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    Dec 29, 2014
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    Thanks guys
    I guessing from what you folks are saying is that I should stick with a original spec. rectifier, the BR102, a 200V 10A. and that the 200V15A bridge rectifier, named: GBPC1502W is not going to help?

    The amp works for a few minutes before it heats up, could that be the solder joints loosing contact because of the heat or is the rectifier defective?
     
  5. #12

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    Sure it will help. It's bigger, isn't it? That gets rid of the heat in the rectifier better.
    However...rectifiers almost never go intermittent. When warm-up = fail, you have different problems. Because I don't believe you have a rectifier problem, just glue a heat sink on the old rectifier. If you have a bad solder joint, prodding the circuit board might get it t reveal itself, but resoldering everything in sight is a good method, too. If that fails to fix it, you'll have to go measuring voltages and such to find out what went wrong.
     
  6. Steallearning

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    Dec 29, 2014
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    Thanks again..
    I want to drain the caps in the amp before diving in and the only resistors I have are 7W 100K will one of these work or are they too big? I read somewhere that it might take longer with large resistors.
     
  7. Kermit2

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    really not needed if the equipment has been off more than one day. very very very few pieces of audio equipment require such precautions. the cap.values in the high voltage areas are not large enough to be of much concern. if you power it and need to work on it again quickly a screwdriver with a clip wire to ground will spark away any leftover charge in the power supply filters.
     
  8. GopherT

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    Just measure the voltage on the caps with your meter and watch the voltage decrease. Once it is under 30v you are generally pretty safe.
     
  9. Steallearning

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    Dec 29, 2014
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    One of the radial Caps has a very slight bulge on the top should I replace it while I'm at it?
    Its blue and marked 10000 uf , 6,3v, 85 degrees C (M), Samwha SG. Can't seem to find the exact one.
    Could someone show me where I can get a hold of one or a replacement?
     
  10. #12

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  11. Steallearning

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    Dec 29, 2014
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  12. #12

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    It looks like you have this figured out. It's only a matter of work to make sure the physical dimensions fit.
     
  13. Steallearning

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    Dec 29, 2014
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    While I'm at it I thought I'd try and fix another Marshall Amp. I'm trying to find a replacement cap. for this one.The installed cap is a very small radial cap the only markings on it are 9202(M) 220uf 35v I've learned that the(M) stands for +-20%

    The schematics call for a 220mf 40v cap Cap3.jpg cap2.jpg how much is 220mF in uF. I a little confused.
    Also the schematics call for 40v.
     
    Last edited: Jan 16, 2015
  14. djsfantasi

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  15. Steallearning

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    Dec 29, 2014
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  16. Kermit2

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    the "m" is just an another way to abreviate "micro".
     
  17. Steallearning

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    Dec 29, 2014
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    resist2.jpg resist.jpg I'm looking for a resistor R4 should I be looking for a 10 ohm to replace this and how many watts should this be?
    Also how many volts do I need on the C1 cap?
     
  18. djsfantasi

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    That's what I originally thought, but... Not to be confusing, "m" is for milli or micro??? All references I see are the the prefix "m" means milli. Sometimes i see a "u" for the symbol "μ", but so far, I haven't seen an "m" for micro. Methinks there's maybe an oops on the schematic.
     
  19. Kermit2

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    my memory still contains images of schematics using "mmf" to designate caps in the pico range. micro micro farads
     
  20. Steallearning

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    Dec 29, 2014
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    Could be an opps... Looking at the schematics and comparing that to whats installed, it looks like "m" means "μ"
     
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