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McIntosh - Hints and Kinks

Discussion in 'McIntosh Audio' started by dewickt, Jul 1, 2004.

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  1. CDinMB

    CDinMB AK Subscriber Subscriber

    Messages:
    130
    Location:
    Melbourne, FL, USA
    Saw someone post a mod of an MC30, adding a 7h choke to the power supply replacing the 150ohm resistor. He showed a fair reduction in 60cycle distortion and multiple harmonics. But, I know from working with vintage fenders that adding a choke can change the overall tone of the amp and at least in that application isn't recommended. What is the experience here with this kind of mod?
     
    Last edited: May 12, 2017

     

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  2. dewickt

    dewickt Will fix about Anything

    Messages:
    3,396
    Location:
    Knoxville, TN
    As I remember it raises B+ giving more power, the side effect is under power it will be less musical on the bottom end with tighter bass.
     
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  3. Pio1980

    Pio1980 AK Member Subscriber

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    26,521
    Location:
    Angel Station, Alabama
    The choke, depending on dcr, should give a somewhat 'stiffer' HV source, tho not as much as with solid state rectification.
     
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  4. eiraved

    eiraved Plane Whisperer Subscriber

    Messages:
    2,251
    Location:
    Antelope Valley, CA
    Invite your two grown sons over when deciding to relocate your MC2500...:naughty:
     
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  5. FauxHall

    FauxHall Super Member

    Messages:
    1,591
    Location:
    Abu Dhabi, UAE
    I've a new-to-me MA6200. I'd love to replace the spring clip speaker connections with modern 5-way binding posts. I can live with two or even one speaker set. Down from the current three.

    Is this a difficult mod for the average shop? Any specific guidance or advice?
     
  6. ColonelKurtz

    ColonelKurtz Are my methods unsound?

    Messages:
    192
    Location:
    Los Angeles California
    Can anyone tell me where the Mac 4300V speaker relays are? Can't even find them in the schematic... Thanks
     

     

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  7. dewickt

    dewickt Will fix about Anything

    Messages:
    3,396
    Location:
    Knoxville, TN
    Relays are on the "Output Processing and Power Supply " section 13 page 45 of the service manual.
     
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  8. lordgarth

    lordgarth AK Subscriber Subscriber

    Messages:
    240
    Location:
    slightly west of trump
    Hi Terry, My Mc225 has static on the right channel only on initial start up. I've tested the tube & also tried another tube, same problem Any idea on where to start?, thanks.
     
  9. Flhrich

    Flhrich AK Subscriber Subscriber

    Messages:
    45
    Location:
    San Francisco, CA
    so, after reading all theses "Hints and Kinks" pages...im going into McIntosh Information withdrawal, not seeing anything since Nov 2017.

    On a serious note, these pages were really helpful and enlightening. Need more !!

    Thank you Terry, for starting this thread and sharing your wealth of knowledge with us.
     
  10. chazix

    chazix AK Subscriber Subscriber

    Messages:
    1,153
    Location:
    Groton MA
    I had the first RF amp (Q2, Mac part number 132-097) fail in my MR77, and it took a little fuss to find a suitable replacement, so I thought I might drop a line here.

    The part is an N-channel JFET, and the voltages on the schematic suggest that its Idss should be about 10mA. Mac semiconductor data on the web says 2N5245 is suitable, but those don't seem to be available any longer from first-tier suppliers. I can't remember what led me to 2N5486, but Mouser still has some of those (not many!) from Central Semi, and it worked just fine. DC bias looked good, it tuned up well, and sensitivity is back to original. I think the 2N5486 pinout is the mirror of the original - not a problem, just something to be aware of at install time.

    Cheers,

    chazix
     
  11. atkinsonrr

    atkinsonrr New Member

    Messages:
    15
    I have done a few conservative mods to my C2200 and MC275 MK VI. Many folks say the later Mac reissues and later preamps sound like solid state. I have heard MC 275s and modern Mac pre's in showrooms and even though I own them, I can see how folks feel this way! Beyond changes to carefully selected NOS tubes here is what I found really helps and ends up with (what I think) is the best of both worlds: extension of solid state and the liquid midrange, listenability and imaging of tubes.

    Get a service manual (includes all schematics) from McIntosh. ID all the caps in the signal path. You will notice there are a TON of electrolytics. Replace those electros with Silmics IIs. Replace the coupling caps (I used Mundorf silver/gold/oil). These were not that expensive as they are only 1.0uf and 0.1uf values. These two changes will probably account for most of the increase in SQ. I also replaced series resistors on the signal path with Riken carbon film or Shinkoh tants, depending on position. Anode and power supply resistors replaced with Mills MRA. Final caps in the power supply bypassed with paper in oil. Oh and BTW if you have a MC275 Mk VI, once you get those schematics, you will see it's WAY different from the earlier re-issues. I have no idea why McIntosh officially said there are no circuit changes but that is total B.S. You will also see, for reasons obvious once you check the schematic, that Mk Vi will sound FAR better via the unbalanced (RCA) inputs.

    Happy modding!
     

     

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