MX114 and MC250 Question

Discussion in 'McIntosh Audio' started by AlTinkster92, Oct 9, 2017.

  1. MACKIE1975

    MACKIE1975 Well-Known Member

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    Normally any cap over 15 years old will have reliability issue. The 40 year old caps will be in spec but can pop anytime.
     
  2. Pio1980

    Pio1980 AK Member Subscriber

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    That's the 'why' of the bypass parity test I recommended as a check of neutral preamp line stage performance.
     
  3. c_dk

    c_dk Addicted Member

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    Now it was decades ago but when I hosted the local Audio Engineering Society's meeting with had Clark's A/B/X demo as it's central emphasis the results were quite revealing.

    1/3 of these card carrying AES members heard no difference ever between a MC752 amp and one from PSE. 1/3 correctly identified which amp was "x" everytime or missed just once. 1/3 were 50/50 or could be a coin flip.

    These people were part of the audio industry and still 2/3 could hear little difference so it would certainly make sense that members of this forum will also not be able to hear a difference.......but some do.

    I find this interesting and worth further exploration and then verification but appropriate testing procedures.

    I have before and after noise spectra scope shots of the last C26 I restored.....

    In the case if the C26 based preamps and preamp tuners the caps that degrade the most are part of the phono stage which this OP does not use.

    I believe it was leestereo who has posted about the "huge" sonic benefits of replacing all the old Mylar caps, I have not verified this and am not sure how to test his results......yet.
     
  4. sberger

    sberger Hard Core Geezer Subscriber

    I'm just going by what I read, which is along the lines of "you'll never hear what that old piece is capable of unless you replace the old caps with new ones". And mind you, I'm not here advocating recapping. I have several old pieces that I like just fine and they are all stock.
     
  5. BilboBaggins

    BilboBaggins AK Subscriber Subscriber

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    I don't think Leestereo posted that. I think it was me. Although I would have to reread the thread to be certain. Ben tends to use more scientific terms.

    However I don't, and I still say there were huge benefits in going through the circuits and replacing all caps in the signal path along with other components where new technology improves the results.

    From my perspective, as the owner of that particular C26, there was a very large improvement. So much so, I sold my restored C24 as a result. I actually ABed a C32 and that C26 when I first got them and I preferred the C26. So I kept it and sold the C32.
     
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  6. Pio1980

    Pio1980 AK Member Subscriber

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    Some overhaul diaries I've read indicate nearly everything but the chassis, heatsinks, transformers and hardware being replaced on the 1st gen S/S Mac amps.
     
  7. avguytx

    avguytx AK Subscriber Subscriber

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    That's "almost" what I'm doing to mine. I ordered new resistors, caps where needed, all new transistors (not for heat sinks yet), two new multi-caps, and two new main filter caps.....just to be on the safe side for my MC250. Preamp wise, I'm using a new one as I've already been through the complete rebuild and upgrade of a Carver C-1 with well documented BillD mods. It was a complete game changer in that preamp once all those old (around 25+ year old) resistors, caps, IC's, RCA connections, etc., were changed out. I won't get rid of that preamp because it sounds so darn good...but it's not in the main system now as I wanted something with built in DAC's versus all the external ones. But that's just me.

    Caps age in everything and it doesn't hurt to change them if a person is so inclined. But if people live by the old saying "if it ain't broke, don't fix it", well, there will come a point they'll be fixing it. Kind of like never changing the oil or spark plugs on your car because you want them to be "all original and OEM". Uh...no.
     
  8. sberger

    sberger Hard Core Geezer Subscriber

    Wonder what Audio Classics would say to this?
     
  9. 62caddy

    62caddy Trust but verify Subscriber

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    Hmmm...slight difference between not changing oil versus not changing spark plugs but the point is taken.

    As with most things, it's a gray area as to what level of performance deterioration a given individual is willing to tolerate which also must be reconciled with the costs associated which also varies according to the individual- his finances, priorities etc.

    In a perfect world, we'd all have wings but that's just the reality.
     
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  10. avguytx

    avguytx AK Subscriber Subscriber

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    Just my opinion and take on things....that's all.
     
  11. Leestereo

    Leestereo Super Member

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    Also prone to degradation after ~40 years, are the small electrolytic capacitors in the C26 power supply (i.e., C307 and C308) and the large carbon composition resistor (R313) that connects the large can capacitors. In the C26 that was on the bench, this 1.5kohm/2W resistor had drifted to 850ohm and caused an increase in voltage by ~20V on C304B (see Restoration and Upgrade of a Late Production C26 for additional details).
     
  12. c_dk

    c_dk Addicted Member

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    I think at this point I believe the OP is just looking for someone, preferably local to him, to correctly restore his unit. I think i remember he had a glass breakage issue earlier.
     
  13. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Yep, going to send this down along with the amp to Dave Gillespie, he''ll get to the bottom of whats ailing the 114 and anything on the 250 as well. Dave redid all 3 of my Fishers and they are quite nice. Lots of good techs out there but I know Dave and trust his abilities and judgement. :) Still, bugs me Audio Classics sent the 114 back the way it was and charged me 393.00. ( I did get e full refund from the owner ) They even said they did a alignment it and the invoice said 16 dollars for that.which means they didn't align a thing. I know a alignment on FM cost a a lot more....

    C-dk I did have to wait for a dial glass as well, they never ordered it and said they did. Gail from Mac parts got me one and I had to inform AC that one was waiting for them...sigh. Thanks for all the help in here! Al
     
  14. Leestereo

    Leestereo Super Member

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    +1
    Dave G. is the man!
     
  15. c_dk

    c_dk Addicted Member

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    Make sure to have Dave check out the MC2505 1964 service bulletins in the AK database. I think he will get a real chuckle as Mac was trying to help the local tube repair techs get comfortable with those new fangled transistors.
     
    Last edited: Oct 12, 2017
  16. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Thanks c-dk, will do! Al
     
  17. sberger

    sberger Hard Core Geezer Subscriber

    Wow...would like to hear AC's side of the story on this.
     
  18. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

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    Indeed. Wonder if your Klipsch speakers are operating to spec? Is the crossover in good order?
     
  19. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Yep, New xovers from Bob Crites on the LaScalas....
     
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  20. KentTeffeteller

    KentTeffeteller Gimpus Stereophilus!

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    Are they placed in corners? And you may like a Cornwall better.
     

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