Vintage Mc275 One Channel Weaker

Discussion in 'McIntosh Audio' started by drillher, Jul 8, 2018.

  1. drillher

    drillher AK Subscriber Subscriber

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    I have a vintage Mc275 that had a total rebuild aside from some of the resistors that were not out of spec.The right channel is weaker.When I reversed the preamp.inputs,the same rt.channel was weaker.Also,the amp.now sounds dull like there is a blanket over the speakers.I had a replacement tubes for all but the 12AT7's and the change made no difference.I ordered two NOS 12AT7's and should have them next week.Hopefully it is one of them.
    Dave
     

     

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  2. TSmith8605

    TSmith8605 Senile Member Subscriber

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    Did you also reverse the speakers to see if the weaker side stayed with the amplifier or the speaker. I assume tweeters are OK.
     
  3. twiiii

    twiiii Addicted Member

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    Seeing How you are close to Audio Classics, I would go pay them a visit. I should be so lucky. Now you know why I own SS. Not that they can't have troubles, too.
     
  4. drillher

    drillher AK Subscriber Subscriber

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    I will try reversing the speaker wires.
     
  5. drillher

    drillher AK Subscriber Subscriber

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    1,676
    Location:
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    I sprayed all of the pots and the input switch,which didn't help much The following day when I reversed the speaker wires,it solved the problem some how.Both speakers are equal now.I'm not sure if cleaning the pots took 24 hrs.to kick in or if there some how was a bad connection on the rt.speaker terminal.Could a wire underneath the speaker terminal,inside of the amp,have a cold solder joint?
     
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  6. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Cold solder joint ? No !
    the problem with very old units is that somebody sometime use a wrong screw to tight the speaker connection and make the output from output transformer shorted to ground
    this is the first thing to double ckeck when you buy an old unit
    check each screw to see if they are identical length
     

     

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  7. drillher

    drillher AK Subscriber Subscriber

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    Thanks for the tip on the screws.Right now everything is working.
     
  8. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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