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Marshall DSP 201

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  • #1

    Marshall DSP 201

    Yes... another Marshall 2000 dsp 201 question. I have read most of the related threads about solder joints, and the famous BRIDGE RECTIFYER.

    I cut and added a heat sink unit to the rectifyer and that little puppy still gets so hot that you can't hold your fingers on the cooling fins after a few minutes. The 4 fins are 1 inch tall by 2 inches long.

    The first time I used it ( after mods. ) it worked for about 10 minutes and the volume and quality began fadding out. I then turned it off for a couple of hours and used it for about 20 to 30 minutes and no issues.

    I have checked/resoldered all suspicious joints. Tubes are all looking great. This amp has an amazing sound. It is my first tube Marshall and I can see why people like them even with the " issues ".

    My question is 1.....where should I install a 12 volt CPU cooler fan and

    2.....how / where to connect it ?

    Thanks for being patient with an " OLD " topic.

    I appreciate the expertise
    DOC STITCHES
    Tags: None
  • #2
    DSP? DSL?

    That bridge provides less than 1 amp to the three preamp tubes.
    It should handle that without a fan. Pull the preamp tubes and fire up the amp. Does the rectifier still get hot? it shouldn;t.
    Education is what you're left with after you have forgotten what you have learned.

    Comment

    • #3
      Hello Doc,
      you might also check that the heater bridge supply filter capacitors are not getting warm, too. They could be leaky & loading down the bridge OR could just be dried up a bit & not working at their optimum uf rating (see final paragraph below).

      BUT...

      My experience with these DC filament supplies in general is that the bridge no only becomes unsoldered, but it also becomes internally intermittent from overheating for soooo long. Also if the diode becomes even slightly internally resistive, it will get hotter than normal.

      I ALWAYS replace the bridge as a precautionary measure. It only took having 2 amps come back for me to make this decision. I'm using a 10 amp bridge replacement from Mouser. ($1.40 @ Mouser# 583-BR108) it is only slightly bigger & fits fine. You should also mount it off the pcb for cooling reasons.

      We had a RadioShack going out of biz here a while ago & I was surprised to find these bridge rects there. BR-108 is the generic number.

      To Enzo's comment about the heaters only drawing 3amps...

      I think the reason these supplies need to be so far overrated with current spec (even than the mfg does) is perhaps because the current draw from a 'normal' B+ supply is not consistently the highest (lower duty cycle) than it is rated for, but only intermittently HIGH. Where as, the heater supplies are expected to supply their highest current ALL THE TIME (high duty cycle...100%).

      This is why I believe you should replace any filament supply rectifier that is failing with higher rated diodes. I replace the 1N4007 diodes in the Mesa's with 3amp variety, stand them off the board & they still get hotter than I would like.

      I suppose if you wanted to get nutz about it, you could also increase the uf rating of the filter caps for the filament supply. That would serve to somewhat relieve the bridge as the filters wouldn't sag so much between conductive cycles...thereby relieving the diodes of some of their work during the conductive portion of the cycle.

      glen
      Last edited by Mars Amp Repair; 04-18-2009, 03:58 PM. Reason: adding more info

      Comment

      • #4
        Originally posted by Enzo View Post
        DSP? DSL?

        Thanks Enzo. I hope to get to that project later today.
        Doc

        That bridge provides less than 1 amp to the three preamp tubes.
        It should handle that without a fan. Pull the preamp tubes and fire up the amp. Does the rectifier still get hot? it shouldn;t.

        Comment

        • #5
          Thanks Glen.

          One more sewing machine and I hope to get to that 201 today.

          I'll see about the BR-108, too at my local Radio Shack.

          Doc

          Comment

          • #6
            Thanks Enzo.
            I put in new 8 amp, 600v bridge and left the legs on and the Marshall works like a charm.
            It now gets only warn....not HOT.

            Doc

            Comment

            • #7
              Hey Glen.

              I put in the new 8 amp, 600v bridge and left the legs on to keep it away from board. The Marshall now works like a charm and the bridge only gets warm...not HOT.

              Thanks again
              Doc

              Comment

              • #8
                Originally posted by Enzo View Post
                DSP? DSL?
                Egad, that got my attention, too.

                My thought was "oh no, Marshall has slapped a DSP board in there."

                -Erik
                Euthymia Electronics
                Alameda, CA USA
                Sanborn Farallon Amplifier

                Comment

                • #9
                  YO Doc,
                  Glad to hear we could help you out...glen

                  Comment

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