JCM 800 2203 MK2 6550 bias question

Discussion in 'The Workbench' started by BobVigo, Mar 7, 2021.

  1. BobVigo

    BobVigo Member

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    I picked this up and from my understanding, the MK2 came with 6550?

    are there bias points in this circuit to take the readings?

    If not, pins 1&8 are tied together, can I put a 1ohm between them and ground for the cathode bias method?
     
  2. South Park

    South Park Well-Known Member

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    In order to take a bias reading you have to measure grid current . That means you have cut the circuit and go through a amp meter . You get a bias probe and put a amp meter in between it and read how many mili amps the grid is using . If the amp is working sounding good then what is the need .
     
  3. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Yes.
     
  4. neikeel

    neikeel Well-Known Member

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    As above
    Don’t try to bias as 30w tubes, if you go to 70%. Treat them as 25w tubes, ie 17.5w at idle.
     
  5. pedecamp

    pedecamp Well-Known Member

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    Watch and learn:

     

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