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  • M100 capacitor replacement



    Hi,</P>


    My 1962/3 ishM100 is way past due replacement of the high voltage electrolytics- so itseems like the sensible thing to get on with it. </P>


    I've noticed a few discussions aboutan oldorgan's muddy sound being down topaper caps in the amplifier, is there a sure fire way I can tell if I have these, in case I can replace them at the same time? The cylindrical caps under the chassis seem to be eitherelectrolytic (x2);or the same red as the generator filters (bar one black one). Theyvary in size,are plastic coveredand have a moulding seam. The values are under 1uF as far as I can see, and the values are printed on along with an "AO" prefix code.</P>


    Thanks in advance for any information you might have,</P>


    Tony</P>

  • #2
    Re: M100 capacitor replacement



    If the caps in question are under 1uf they are probably not electrolytics. If they are coved in plastic they are not paper caps. You only need to replace them if they are leaking DC to the tube grids. I doubt this is the problem with your muddy sound. I would start by only replacing the filter caps which are the can-type mounted to the chassis. Leave the amp coupling caps and TG caps alone until you hear the improvement of the mains filter caps. You may decide that is a big enough improvement. </p>

    If you have the red generator caps your organ is probably made after 1962. Again these are not paper but styrene. Not going to the likely culprit of a muddy sound. </p>

    I have paper caps in my L-100 (early 1963) and muddiness I had went away when I added a dual rotor Leslie speaker. The tends to be a more satisfactory fix then recapping the entire TG.
    </p>

    Comment


    • #3
      Re: M100 capacitor replacement



      Tony-</P>


      I own an M-143 and "care" for two others. None of these organs have yet to experience capacitor problems &lt;knocking on simulated wood&gt;. Unless you are hearing a definite 60 cycle hum from the speakers, I would't bother with that. If you are experiencing a deterioration in sound quality, tubes are the first suspect. Without a tube tester, I'd suggest replacing them as a set. Several vendors sell sets for the AO-29 main amp as well as sets for whichever of the three different reverb amps you might have. Fresh(er) tubes canmake a tremendous difference. Just my humble 2 cents.</P>


      John</P>

      Comment


      • #4
        Re: M100 capacitor replacement

        [quote user="bluetantra"]


        Tony-</P>


        I own an M-143 and "care" for two others. None of these organs have yet to experience capacitor problems &lt;knocking on simulated wood&gt;. Unless you are hearing a definite 60 cycle hum from the speakers, I would't bother with that. If you are experiencing a deterioration in sound quality, tubes are the first suspect. Without a tube tester, I'd suggest replacing them as a set. Several vendors sell sets for the AO-29 main amp as well as sets for whichever of the three different reverb amps you might have. Fresh(er) tubes canmake a tremendous difference. Just my humble 2 cents.</P>


        John</P>


        [/quote]hello, first post here I think...this is not accurate, electrolytic filter caps have a life span of 5 years at best...you don't have to, or want to wait to hear 60 cycle hum to replace them...any tube amplifier in general that is 40 + years old should have fresh caps put in the power supply for several reasons...especially since you can get the exact mallory replacement nowadays</P>


        I can tell you what the differencewill be when you replace these caps, I've done it many itmes, most multi-caps are certainly not working after 40 years, or have drifted way up in tolerance, in hence over-filtering, which adds bass and mud....replace them and you will hear MUCH better clarity and fidelity...the difference is not subtle!</P>


        also replace thethree 25 uF bypass caps in M series AO-29 amps...when replacing the one in the persussion section I guarantee your percussion will be clearer</P>


        this shoud be done in the leslie amp as well! But leave all CD coupling caps intact please</P>


        re tubes, a tube tester does not put the sufficient voltage on the tube being tested...you need to need to test voltages in the ampto ground, and if the voltages are too high over spec than the tube is most likely weak...if you're not electronically inclined then just swap with known good tubes and listen...hopefully you have a goodear :)</P>
        <P mce_keep="true"></P>
        <P mce_keep="true"></P>

        Comment


        • #5
          Re: M100 capacitor replacement



          You should replace the electrolytics as soon as you can. They might not just slowly go awry, they can fail in a spectacular fashion and take out the transformer and a few tubes with it. </P>
          <P mce_keep="true">I'm hesitant to lable the active life of an electrolyitc. The lifespan of electrolytics is often random. I've seen radios from the thirties that didn't have the slightest noticeable hum, and I've had transistor radios from the seventies that were badly in need of an electrolytics change. Although though the former case is rather rare (It's hard enough to find a set without broken bakelite, let alone one with working electrolytics).</P>
          <P mce_keep="true">It really depends on how well the cap is made, how old it is, how long it was designed to operate for, and how often it was used. So ultimately, you just never know!</P>

          Comment


          • #6
            Re: M100 capacitor replacement



            I still stand by my original diagnosis of re-tubing the AO-29. Whenservicing ANYTHING, eliminate the easy stuff first. Yes, electrolytic caps do fail and can cause extensive damage when they do. Yes, they do have a limited lifespan. Even so, tubes categorically fail more frequently than the caps. It is for this reason that they are so easy to replace where the vast majority of electrolytic caps are riveted onto the amp's chassis and the connections soldered, with Leslie amps being the exception.</P>

            Comment


            • #7
              Re: M100 capacitor replacement

              [quote user="Anthony Meads"]


              </p>

              I've noticed a few discussions about an old organ's muddy sound being down to paper caps in the amplifier, is there a sure fire way I can tell if I have these, in case I can replace them at the same time? The cylindrical caps under the chassis seem to be either electrolytic (x2); or the same red as the generator filters (bar one black one). They vary in size, are plastic covered and have a moulding seam. 
              </p>

              [/quote]</p>

              In circles of folks who regularly restore vintage electronics, the plastic molded caps you are referring to are affectionately known as BBODs -- Black Beauties of Death (one of the trade names for these is "Black Beauty".  They do become leaky with age and ought to be replaced with Orange Drops or other modern poly/mylar cap if you're doing a general overhaul anyway.  You can certainly test each one if you have access to an appropriate cap tester that will measure leakage current, but they're inexpensive and it's just as cost effective to replace them all and be done it.  And an early 60's production date is getting to an age where leakage in these molded paper caps could be a problem.</p>

              Comment


              • #8
                Re: M100 capacitor replacement



                Thanks for pointing that outGrant. I'd completely forgot about black beauties. If you take one of these apart you will see itspaper inside. I don't seem them much because most radios I work on were built in the late forties at thelatest.</P>


                There are lots of people out there who thought broken radios could be fixed be replacing the tubes, only to find that it didn't change athing. </P>


                Capacitors are cheaper. Do those first. If a tube fails, a tube fails. If cap fails, other things go with it. </P>

                Comment


                • #9
                  Re: M100 capacitor replacement

                  Thanks everybody! I replaced the can capacitors, followed by the electrolytic bypass caps in the amplifier. The organ sounds great- much brighter, with a sparkling 1' drawbar! I couldn't necessarily hear an improvement after the second lot of replacement in the amplifier,but at least I have peace of mind for the next 5 years. I didn't in the end replace any non-electrolytics, the only two paper caps were not leaking DC, and doing menial tasks anyway.

                  Comment

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