Do Black Plate 6L6 Tubes Cause Red Plating in Mac Amps?

Discussion in 'McIntosh Audio' started by AA6U, Apr 9, 2018.

  1. AA6U

    AA6U Member

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    Given all of the input, it would seem like the black plate warning is an urban myth. Maybe sasquatch or Santa Claus started the rumor.
     
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  2. AA6U

    AA6U Member

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    Riverside, CA
    And so all of the MC30s and MC240s with black plate 6L6GCs went on to delight happy listeners with their alluring sound for many wonderful years without red plating, and they all lived happily ever after...
     
  3. 62caddy

    62caddy Trust but verify Subscriber

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    ...or 7027(A) in MC240, 1614 (metal casing) in MC30...or 6L6GC (MC240 & MC30) regardless of manufacturer, regardless of whether the plates are colored gray, or black. Yes, all will work in a Mc and work well because it IS a Mc. :)
     
    Last edited: Apr 15, 2018
  4. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    Not to nitpick but '6L6', while certainly an early - in fact THE earliest - version, is not a glass bottle tube. This was pointed out earlier in the thread but I just wanted to make sure everyone reading this was clear on it so there is no confusion. But as you said, it won't work in a Mac amp and that was the point.

    [​IMG]

    Sometimes people will put an M after the tube number to designate metal envelope. These are also sometimes called 'smokestacks'. I always wanted to build a PPP amp with a bunch of these - they are pretty cheap as 6L6 goes. But who am I kidding, I never have time to build amps...
     
  5. 62caddy

    62caddy Trust but verify Subscriber

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    Isn't the 6L6 the same as the 1614?
     
  6. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    No. 1614 has a 500V max plate voltage, 6L6 is 400, for one thing. Plate dissipation is also higher in the 1614.
     
  7. Steve O

    Steve O Super Member

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    Location:
    SE MI
    For the most part yes, but.......a 1614 is a “selected” 6L6 for transmitter service and carries slightly higher ratings as a result of selection. Not sure just what parameter(s) is selected for.

    From RCA HB3:
    Max (CCS)
    Plate=375V / 21W
    g2=300V / 3.5W

    Max (ICAS)
    Plate=550 / 25
    g2=400 / 3.5

    6L6
    Max
    Plate=360 / 19
    g2=270 / 2.5

    Curiously, some 1614s show their 6L6 heritage.

    Above the flange:
    [​IMG]
    Below the flange:
    [​IMG]
     

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  8. tuberadios69

    tuberadios69 AK Subscriber Subscriber

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    Location:
    Virginia
    You CAN NOT use 7027A tubes in an MC-30. The tube will short the amp. Incorrect pin out in the tube socket. (Or is it one extra pin used?) Trust me, I know from experience (several years ago). On the other hand, 7027A's work fine in an MC-240 amp.
     

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