Recapping/Updating a C26

Discussion in 'McIntosh Audio' started by 4MarkNY, Mar 7, 2012.

  1. 4MarkNY

    4MarkNY New Member

    I've got a c26 preamp that I use along with a rebuilt Dynaco ST-70, a Sansui tuner, and a couple of turntables in the basement studio ( Sonny #3, 17 is a keyboard player, and down there are a Hammond M3, Leslie, drum kit ( Boy #4)). I've learned to do these things myself over the last couple of years, without spilling too much blood....The Dynaco has a new VTA driver board, upgraded power caps, running Genelex Gold Lion KT-66s. The Hammond and Leslie 145 have been gone through, with some updates as well. My point here is that I've some experience bringing some old, barely working stuff back to life, but I'm no electrical engineer or circuit designer. I enjoy the challenge of making these devices sound better, and learning some fun skills too.
    Note: This post cut off and timed out before I finished, so I'll go back in and re-create again......

    The C26 works fine. , but it was built between '68 and '77.
    I have limited time, resources, but would like to attack areas that will give me most bang for the buck.
    Electrolytics? coupling caps? where should I spend my energy and $, since I will not be replacing 100% of the caps on this foray.
    Last edited: Mar 7, 2012
  2. dshoaf

    dshoaf That high voltage buzz Subscriber

    Suggested approach:

    - Rebuild power supply - electrolytic caps, etc, then confirm it is developing regulated voltages to spec.

    - Next, clean all the controls but you've already discovered how that helps.

    - Then move on to coupling caps. I'd suggest you start with the line stage first and work backwards from the output. Priorities for replacement are: 1) electrolytics, 2) any caps directly in the audio chain, then 3) film caps in the feedback loops.

    - If you're into vinyl, then follow the same approach for the line stage but now in the phono preamp.

    - Lastly, pay attention to the grounding of the RCA jacks, wire runs and drain wires used to connect all the parts. These are known to break while working on them. Similar to the C28, they are also known to cause hum and noise problems. Search around here for discussions on the C28 wiring issues and how to address them.

    Hope that helps.


  3. skippy_ps

    skippy_ps AK Subscriber Subscriber

    Bought mine a few years ago as a non-working unit. Filter caps were toast and a shorted transistor in the phono stage. Replaced the transistor and filter caps (new snap-in caps on top with the smaller values underneath) and got it up and running.

  4. Gregory

    Gregory Radical Lab Animal

    Could you describe the snap-in caps on top more? Thanks

  5. skippy_ps

    skippy_ps AK Subscriber Subscriber

    There's an old thread here but I doubt that I can find it. Should have the pics at home and I'll dig them up.

  6. 4MarkNY

    4MarkNY New Member

    Thanks, DS. That appears to be a sound strategy.
    I forgot to ask during my re-write of the disappearo portion of the post...Are there mods that are popular when re-conditioning these? Increased capacitance if the filter caps? any known and reliable modifications? (I'm not a purist....)


  7. dshoaf

    dshoaf That high voltage buzz Subscriber

    I'd recommend getting it running first in stock form. You can try tweeks on it, of course, but I know of no well-accepted or well-proven mods to many of the Mac pieces. They were well-engineered to begin with!

    Besides, you can't really know if sort of mod does any good unless the piece is back up to spec.


  8. skippy_ps

    skippy_ps AK Subscriber Subscriber

    First pic shows the snap-in caps from the bottom including the two brown caps tacked on underneath.

    Second pic shows the new filter caps glued on top. Used hot glue but it didn't really stick very well to the sleeve over the caps.


    Attached Files:

  9. c_dk

    c_dk Super Member

    I found that taking the volume control apart and burnishing the wiper inner cotact surface (NOT THE CARBON) makes a world of difference.
  10. Gregory

    Gregory Radical Lab Animal

    NICE!! where do/(did) you get those caps?

    Are the lower caps held in place by adhesive pad tie-wraps? Maybe the OP can be located? Search C26 Murray?

  11. skippy_ps

    skippy_ps AK Subscriber Subscriber

    I'm sure they came from Mouser. The ones on top are something like 450v so they'd be big enough to fit on the fiber thingie on top of the chassis. The ones underneath are tie wrapped to a one of those stick on pads and of course are much lower voltage. I tried to pick something pretty close to the original capacitance of the original twist-tab caps.

    As far as using the snap-in caps, it's actually pretty easy to wrap the wire around and solder. Makes a pretty neat looking connection. I did have some trouble getting all of the connections tied to the negative lead on one of the "on top caps." It might have worked better to use a solder lug in between the cap and wires.

  12. Gregory

    Gregory Radical Lab Animal

    Sorry I'm not too clear on "snap in" caps and what that involves.

    How did you mount the 450V caps on top to the dielectric mounting rings/washers?

  13. skippy_ps

    skippy_ps AK Subscriber Subscriber

    Snap-in caps have bent legs, probably made from flat, zinc plated steel, and are made to be pushed into a pcb and they snap in place. The bent leg then holds them in.

    I just glued the big caps down but it didn't work very well. About the only other thing to do would be to drill and tap the chassis and use a clamp.

  14. 4MarkNY

    4MarkNY New Member

    Recapping a C26

    Well, this is a fine kettle of fish, but I suppose that you guys knew this all along....This being my first adventure to McIntosh land...
    Starting in the power section, I identified a pair of multi section electrolytics that would likely succumb to age, etc in this preamp. There are two of them C304 & C305, with odd values....both are 160/200/200/150V multisection caps, from their description in the parts list. Of course I can't find a google hit for anyone supplying these. At mouser, I can find 161uf electrolytics, but $28.00 apiece at low volumes ( several of the "161s" have minumums of 40 units....)
    CE Manufacturing, who apparently has the old Mallory Machines, doesn't have anything that comes close.
    I'm a bit surprised, since I would think that there is a business opportunity to supply these odd ball multisections to the McIntosh community, but I can't find them. Looks like the standard procedure with this preamp is to await a failure, and then re-stuff the can if you can find correct valued componentry.
    Or perhaps there are other solutions someone can suggest. It looks like a pre-emptive strike to put this device up to snuff is a bit more adventuress than I would have thought.
  15. skippy_ps

    skippy_ps AK Subscriber Subscriber

    Once you get past the fact that there are no twist tab cans to use, there are a variety of ways to take care of this. Axial or radial caps underneath, or clean out the old cans and insert maybe one cap inside each can and two more under the chassis. Note that C305 can be 100v, which would be a smaller cap called for in the schematic.

  16. c_dk

    c_dk Super Member

    There are many caps that need to be replaced so do not get hung up on the unobtanium ones...the multi section caps will need to be replaced with multiple singles as described.

    I have made up boards for them, stuffed and added them to the existing....we must be creative just like the car restorers are when the rebuild old mscle cars.

    I have been testing the pencil style Nichicons ( as well as the more standard size) for higher voltage multicap replacement with good results.
  17. 4MarkNY

    4MarkNY New Member

    Recapping C26

    That's more do-able... I thought from looking at the parts list that this was a 3 section can, but from the schematic I see that there are only 2 sections, so that's better. one is a 160uf at 200v, the other section 200uf at 150V. I was thinking that I'd have to pair (2) 80uf caps to get the 160, and then 2 more at 200....(making a bundle of 8 to replace the 2 multisection cans....)

    The way the parts list shows, I was thinking they meant: 160/200/200 @150V
  18. scottman5044

    scottman5044 New Member

    mcintosh c26 preamp problems

    Ok, so this is my first mcintosh equipment, i just recently bought a c26 and mc2105 at my pawn shop. I was so excited to hook it up and listen to it, and was disappointed when i did because there was this annoying hum coming from the speakers. I isolated it to the preamp, by changing amps preamps and cords using process of elimination. So the hum is a constant noise that doesnt change with the volume knob. I talked to a professional mcintosh repair guy and he said it was probably the 70v power supply filter capacitor. Not sure which one that is Im guessing the big silver (one)s in the center? I have worked on arcade machines and done small repairs before but I am really gonna need some help on this one. First I would like to know what needs to be replaced, would like to keep it close to original but will do whatever it takes to get it working right. Second where can I get the parts? Sorry I know im asking you guys to hold my hand threw this but I am a poor pawnbroker that cant afford a rebuild by a pro. Thanks
  19. c_dk

    c_dk Super Member

    Welcome to AK...and thanks for being honest about your situation.

    The vintage preamp you have will always need lots of detailed repair...many small items need to be addressed..there is hardly a silver bullet 1 item to replace to make it right.

    Assuming your local Mac guy is allowed by his boss to do restoration, and has the additude to do restoration work, I suggest you give him a budget and prepare both units for value added resale.
  20. scottman5044

    scottman5044 New Member

    well, did my homework on capacitors and downloaded the schematic for the pre-amp, replaced the capacitors with new ones. Had to get a little creative with where i was gonna put them. I left the original capacitors on top, and just snipped the wires to them and soldered them to the new capacitors underneath. So if you take the top cover off it still looks original, and if I could find the original capacitors I could easily make it back to original because I did not modify anything in the case. Turned the pre-amp on with my fingers crossed and no more annoying hum!!!!! It sounds a lot better than the pre-amp I was using. Anyway thanks for the info guys.

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