Mcintosh C28 restoration

Discussion in 'McIntosh Audio' started by rg3117, Jan 18, 2018.

  1. rg3117

    rg3117 New Member

    Messages:
    32
    Just a quick update to say that following Hunted11’s advice, I cleaned the input selection switch with DeoxID, removed oxydation from the RCAs, and the phono inputs magically reappeared. They had probably not been used in decades, if ever. Same with the Tape pushbuttons, which I have managed to push all the way in until they clicked. Still harder that the other buttons though. I am keeping them pushed in for now, rotating between one and the other from time to time. Looks like this unit has not been used in a very long time. Tomorrow I will call Mcintosh, and see if they still have the glass in stock.
     
    Last edited: Jan 21, 2018

     

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  2. rg3117

    rg3117 New Member

    Messages:
    32
    Input/stereo mode selector light bulbs

    I haven't found a lot of information on those, except here:
    http://audiokarma.org/forums/index....-to-replace-input-mode-selector-bulbs.705686/

    Mcintosh part number is 058-041. These are 6V, 'grain of wheat' bulbs. Given that I also need the LED lights for the front panel, I purchased this on Ebay:
    https://www.ebay.com/itm/McIntosh-C28-Preamplifier-Custom-LED-Upgrade-Kit-Complete-Illumination-Kit/192426120241?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649

    After trying a number of different LED bulbs for my MC2505, this is the only vendor who provided LED lights that actually worked. The problem I was having in particular with the MC2505 is that the red square above the Mcintosh logo would not light up, either because the bulbs were not long enough to provide light through the diffuser, or because green light will not go through a red filter.

    I am adding some picture of the 'grain of wheat' light holder. The black plastic parts slide off the shaft of the switch, with a little persuasion.

    On another subject, it looks like neither Mcintosh, AudioClassics nor McintoshAudio have any C28 glass in stock, so C28 owners beware, don't break any glass! I have one on back-order with Mcintosh, but it may take up to 6 months to arrive... In the mean time I will try to repair the one I have and use it as mock-up for my project.
     

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    Last edited: Jan 29, 2018
  3. rg3117

    rg3117 New Member

    Messages:
    32
    Received my order from Mouser today with the electrolytics caps. I got a selection of Nichicon HE and CY for the power supply, and Nichicon KA, KZ and FG mostly for the boards. There were a couple of odd values for which I had to look elsewhere, and a TVA ATOM for the axial cap. I am attaching the list that I have used, if others are interested.
     

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  4. rg3117

    rg3117 New Member

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    32
    Also got to clean the RCAs at the back. I used Brasso and a rag wrapped around the empty body of a pen. This looks really nice, I am starting to rethink the gold plated RCAs option.
     

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  5. rg3117

    rg3117 New Member

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    32
    I took a moment today to slit one of the heat shrinks open on a ground drain, and found out that I have one of the old harnesses with the ferrules, and that they don’t seem to have been soldered. Need to add that to my To Do list. This will take some time, although my understanding is that only the ones that have two cables joined by a ferrule needs doing.
     

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  6. rg3117

    rg3117 New Member

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    32
    I drilled through the rivets holding the large cans in place tonight, and unsoldered the two 3,000uF caps. Could not resist to open them and look inside. I think surgery was overdue!
     

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  7. Hunted11

    Hunted11 Active Member

    Messages:
    150
    Location:
    Western Massachusettes, USA
    Did you have to heat them to get the cans off????
     
  8. rg3117

    rg3117 New Member

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    32
    No, they came off easily with some twisting. There was some tar on the top half of the can, but it looked very dry.
     
  9. Hunted11

    Hunted11 Active Member

    Messages:
    150
    Location:
    Western Massachusettes, USA
    Thanks. I have just gone through my MC2100, Carver PM 350 and a Teac r2r and Tandberg cassette deck. Now I want to attack my C28 and MR73. I'm just trying to decide to re stuff or order from Hayseed.
     
  10. rg3117

    rg3117 New Member

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    Do they make a kit for the C28, or would that be a custom job?
     
  11. Hunted11

    Hunted11 Active Member

    Messages:
    150
    Location:
    Western Massachusettes, USA
    They don't make a kit that I know or but I know a tech in Ct that has used them for Mac's and other amps and he says they are reasonable.
     
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  12. rg3117

    rg3117 New Member

    Messages:
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    With the capacitors on the base. I drilled through the base with a small diameter drill bit, close to the connectors, while respecting the spacing between the leads.
     

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  13. rg3117

    rg3117 New Member

    Messages:
    32
    The 3,300uF caps are back in place, held by small bolts. This has already made a big difference in the amount of white noise I was getting at full volume. I will do the multi-section caps next, but need small diameter heat shrink tubing to isolate the leads.
     

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    Last edited: Feb 6, 2018
  14. rg3117

    rg3117 New Member

    Messages:
    32
    Installed the LED bulbs, they are very bright! Also replaced the ‘grain of wheat’ bulbs.
     

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  15. rg3117

    rg3117 New Member

    Messages:
    32
    Found time to tackle the multi-section caps today. This time I had to heat the Mallory can with a hair dryer to melt the tar.

    Same method as the previous capacitors otherwise. Just need to be careful to assign the correct capacitance to the correct pin. I used hot glue to hold them together and to the base. Also used cold weld to glue the can back to the base.
     

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    Last edited: Feb 11, 2018
  16. McGuyDF

    McGuyDF New Member

    Messages:
    32
    Location:
    Chicago
    Regarding the glass, call McIntosh ASAP, as they only do runs when they have enough orders, could be 3-6 months easily. I got lucky with a 2105 glass, someone cancelled their order the same day I called, $130 and I had it in a week. Or try audio classics, they may have one. I bought my C28 off ebay and it sounds great but I will take it to my local guy for servicing soon since he isn't expensive and he's quick.
     
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  17. showett

    showett AK Subscriber Subscriber

    Messages:
    144
    Location:
    NW burbs IL
    Definitely grab the glass if it's available now. I went with Tom Manley from Mcintosh audio for my 2505-2 and couldn't be happier. Good luck with it and will be following your lead with my C28 very soon.
     
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  18. rg3117

    rg3117 New Member

    Messages:
    32
    I called McIntosh, Audio Classics and McIntosh Audio but unfortunately nobody has any C28 glass in stock right now. I am gonna have to wait.
     
    Last edited: Feb 11, 2018
  19. McGuyDF

    McGuyDF New Member

    Messages:
    32
    Location:
    Chicago
    order the glass now regardless so you're in the cue for it.
     
  20. twiiii

    twiiii Addicted Member

    Messages:
    5,767
    Location:
    west Texas
    I HAD A C-28 FOR 5 OR 6 YEARS between my C-22 and C-29. The C-28 was a touch warner than my C-29 in the phono section. But I got tired off the mis-tracking master volume control, which there is no cure for and having to clean all the trim pots and controls to keep things quiet. So when the C-29 was talked about I ordered one. I got the 77 th one built and enjoyed it for over 30 years until replaced with a C-34. Having gold chassis RCA connectors is another step up to cut down on intermittent issues. I'll never go back to a Mac pre-amp with stepped controls again . The steps are to large and the controls are always noisy with out semi annual care. Only the balance control needs attention on the C-34 has been my experience over the last 10 years until the EQ selection switch went south on me. Then the guys at Audio Classics rebuilt it for me. A C-28 is a great unit far surpassing its specs below 4 Khz by a wide margin and does a very good job in the high freq, spectrum, . Its not capable of what a C-33 or later units can do but for most applications its a very outstanding unit. If you are willing to maintain it. Its all a matter what lengths you are willing to go to keep your system up to snuff. My MC 2505 is my second oldest Mac piece at the moment at 46 years old. Clean switches and controls once a year has kept it working and performing very satisfactorily. So good luck with yours. You might want to fabricate a piece of metal to separate the left and rings sections of the phono circuit preamp card to improve cross talk. Davie Obrian installed mine for me when my C- 28 was about one year old. .I went back and looked at your pictures,you do have the divider. Pardon me>
     
    Last edited: Feb 16, 2018
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