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MR55A Thoughts

Discussion in 'McIntosh Audio' started by smartin53, Apr 13, 2018.

  1. smartin53

    smartin53 Well-Known Member

    Messages:
    531
    Location:
    Denver
    So I got an MR55A for cheap and am in the process of restoring it. The thing must have sat in an attic or barn for years as it was in terrible condition visual wise. Definitely needs a recap also (one of the bumblebees is visibly split).

    Two things I was thinking though. The brass finish is badly pitted and corroded. I'm thinking it might be best to just sand it and give it a brushed look instead. The paint is not good either so I might just repaint that and carefully repaint the lettering too. Anyone done this before?

    Also, how tight is the tuning mechanism supposed to be? On newer stuff you can kind of spin the tuner, but this one there is a bit of resistance even though it moves freely.

    mr55 1.jpg
    mr55 2.jpg
     

     

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  2. smartin53

    smartin53 Well-Known Member

    Messages:
    531
    Location:
    Denver
    OK so another question. I got the offending caps replaced (I haven't installed the new multicap just yet), installed missing tubes, and did a general cleanup. I turn the unit on and all tubes and bulbs seem to power up fine, but I get zero audio output. Not a single click or hiss from stations whatsoever so it definitely appears to be something with the audio output itself. Any simple things I can check right off the bat?
     
  3. rollcentre

    rollcentre Boom-tizzz

    Messages:
    523
    Location:
    DFW,TX, United States
    I've got an MR55, and I haven't had the opportunity to play around with it yet, test the tubes, recap, replace selenium etc., mine somewhat works, but I haven't powered it up since the previous owner demoed it to me. for the tuning knob, mine takes a very slight amount more effort to turn, compared to my mr78, but it really does turn quite easy compared to my '58 RCA 8-rf-13, has a better overall feel and way less backlash.

    IMG_20180317_225039.jpg
     
    ossidian likes this.
  4. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,212
    Location:
    France
    Hello smartin53

    I think that you didnot realize how much this task is complicate and is a very long process . A unit in this shape can't work . Don't forget also that this kind of unit is not only a chassis with empty tubes sockets , but there is also mica capacitors inside each IF transformers and they need to be refixed and at the end realignement of this tuner is necessary ....

    I know about I am talking about because I am doing this for a customer who asked me to make his MR71 like brand new , I already spend over 6 month and it is not finished ....Very , very long process
     
    rollcentre likes this.
  5. smartin53

    smartin53 Well-Known Member

    Messages:
    531
    Location:
    Denver
    Well 6 months later I finally got back around to the unit. Turns out the problem was rather simple. The rectifier tube and audio output tube simply were not making proper contact. Dunno how I missed that the first time. I cleaned up the sockets again and now it passes audio and picks up stations fine. I went ahead and finished up the recap to include the mulicap can while I was at it.The only issue I can find with it now is the meters don't do anything. They lock into a position once the unit warms up and stay there. They do bounce around when switching between AM and FM but then return to their prior position.

    I also went ahead and installed the new glass I got from RadioDaze and started to strip the faceplate for a refinish. Ultimately once I got all the paint off I realized I really like the raw rough brass look. Decided to just stick with that for now. It's only a mono unit but they kindly included 2 outputs so I just used both for L/R channels. I'm not too picky about stereo sound for radio sources so that's fine for me. It goes well with my setup so I can now retire that goofy "elegant" solution I had before using a sony watchman. Tuners really do look best in the dark ultimately tho.

    IMG_7336.jpg IMG_7340.jpg IMG_7346.jpg
     
    ossidian likes this.
  6. Jay321

    Jay321 New Member

    Messages:
    1
    The tuning meter and sensometer are controlled by the two 6BN8 tubes. Try cleaning out those sockets and test the tubes. Mine is super fussy about those two tubes so they need to be quite strong. After that you should download a service manual and do alignment. My manual is actually labeled "Alignment Manual". Adjustment for meters is in that manual. Just remember you need non-conductive tools or you might get zapped.

    Hope this helps. This is my favorite tuner of all I've owned. I live in a deep valley and most tuners pick up mostly nothing. The mr55a picks up everything and sounds just outstanding.

    P.S. This is my first post. Hee Hee.
     
    ossidian likes this.

     

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