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McIntosh MC60 Power Amp Power Supply Question

Discussion in 'McIntosh Audio' started by Hi-FiGuy, Jan 13, 2018.

  1. Hi-FiGuy

    Hi-FiGuy AK Subscriber Subscriber

    Messages:
    574
    Location:
    Southern California
    I have noticed that this amp has 80uF of capacitance right after the two 5U4 tubes. Wouldn't this amount of capacitance cause arcing of the rectifiers? Has anyone changed this when replacing the capacitors in this unit? Would it be better to reduce the input capacitance? I plan to replace the capacitors and could reduce this value to 60uF or lower.

    Thanks
     

     

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  2. dewickt

    dewickt Will fix about Anything

    Messages:
    3,395
    Location:
    Knoxville, TN
    With 2 rectifiers in parallel and a perfect transformer you are safe to 80 uF, calculating in the transformer impedance the capacitance con go to well over 100 uF for 2 tubes. I have seen 680 uF used for the first filter with no apparent problems, though I would not recommend it. The number given in the RCA tube manual is the safe capacitance for worst case design.
     
  3. Hi-FiGuy

    Hi-FiGuy AK Subscriber Subscriber

    Messages:
    574
    Location:
    Southern California
    Ok, I will replace the power supply caps with the same value. This brings me to another power supply question, I have 2 amps I am recapping and I noticed that one has the selenium rectifier for bias and the other amp has what looks like an early silicon unit. In order for the bias supply to be the same can I just replace them with 1n4007 diodes? Thanks in advance.
     
  4. TR6man98

    TR6man98 Well-Known Member

    Messages:
    734
    Location:
    Seattle, WA
    That is exactly what I've done.
    On both of my MC60 selenium rectifier was replaced with 1N4007 and resistor to drop the voltage to specified.
    Away from home to check my notes and value but Terry recommended it and was spot on.
     

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