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Mcintosh MC30s Restoration (Looking for correct schematic)

Discussion in 'McIntosh Audio' started by Tysen, Jan 9, 2017.

  1. x3workshop

    x3workshop AK Subscriber Subscriber

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    The CL- 80 has no bearing on the ratio.

    You can try adding the resistors in SERIES to determine the value, but don't do that permanently.
     

     

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  2. Tysen

    Tysen AK Subscriber Subscriber

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    Okay great. In series!



    I changed the 12ax7, and at 110v on my variac all voltages are within spec for both amps. Including -46 on the output tubes, and -46 on the 12ax7. All at 440v

    Is it necessary to change resistors, or can I just run my variac at 110v? Again, my transformer is at 125v
     
  3. Pio1980

    Pio1980 AK Member Subscriber

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    Your transformer at 125 VAC should be fine. Can't say abt CL80, as the were only used on the solid state rectified amps, afaik.
     
    Last edited: Jan 30, 2017
  4. x3workshop

    x3workshop AK Subscriber Subscriber

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    Agree with the above. Using the CL-80 will just give it an even slower initial startup and drop your line voltage by a couple volts.
     
  5. Tysen

    Tysen AK Subscriber Subscriber

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    Location:
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    Gotcha.


    Just to be clear, I'm fine using the 470ohm resistor in series with the diode, since everything is good at 110v. And I don't need to change the voltage tap on the transformer, right?
     
  6. Pio1980

    Pio1980 AK Member Subscriber

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    Check the heater bus twin for 6.3 VAC to confirm. If high, go to 125VAC tap.
     

     

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  7. x3workshop

    x3workshop AK Subscriber Subscriber

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    I'm not disagreeing with PIO1980, but I think you'll find yourself in a better zone using the 125v tap with the CL80 in the long run. LA tends to have some pretty wide voltage swings.
     
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  8. Tysen

    Tysen AK Subscriber Subscriber

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    Sounds good. Thanks for the LA tip!


    The transformer is already hooked up to the 125V. What I'm wondering is, is it okay to run the amps off my variac at 110v while the transformer 125v tap is being used. ?
     
  9. x3workshop

    x3workshop AK Subscriber Subscriber

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    Yes, It's fine to do that, but if you are going to run it off of a variac permanently you might as well just go back to the 117v tap.
     
  10. Pio1980

    Pio1980 AK Member Subscriber

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    With the variac, but why bother? He best just wire it 125 volt tap and leave it be, imo.
     
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  11. Tysen

    Tysen AK Subscriber Subscriber

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    Location:
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    Right. At 117, my voltages are at 440 & -51ma on the output tubes. That's why I'm wondering about running it at 110, where both amps currently perform at 440 and -46.
     

     

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  12. Pio1980

    Pio1980 AK Member Subscriber

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    Again, look at the heater lines, you want 6.3 VAC or close thereabouts.
     
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  13. Tysen

    Tysen AK Subscriber Subscriber

    Messages:
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    At 110v from the variac, I'm at 6.4 VAC.
     
  14. Pio1980

    Pio1980 AK Member Subscriber

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    Have you tried the 125 tap?
     
  15. Tysen

    Tysen AK Subscriber Subscriber

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    The amps are currently hooked up to the 125v tap.
     
  16. Pio1980

    Pio1980 AK Member Subscriber

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    So, putting 110 VAC into the 125VAC tap yields near correct voltages?
    Is that 110 VAC measured or by the dial on the variac?
     
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  17. Tysen

    Tysen AK Subscriber Subscriber

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    Correct, putting 110v into the 125VAC tap yields correct voltages. That's with the 110VAC dialed on the variac...I didn't measure it actually.
     
  18. Pio1980

    Pio1980 AK Member Subscriber

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    Try measuring it at the amp. I'm very interested in your project's success.
     
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  19. x3workshop

    x3workshop AK Subscriber Subscriber

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    Likewise!

    Curious what the voltage actually measures.
     
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  20. Tysen

    Tysen AK Subscriber Subscriber

    Messages:
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    I appreciate your investments. I seriously couldn't of done this without you!

    When I get home this evening, I'll test the voltage from my variac and report back.
     

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