68' Super Reverb question

Discussion in 'Shock Brother's DIY Amps' started by rpcruab, Feb 13, 2009.

  1. rpcruab

    rpcruab TDPRI Member

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    Sorry in advance for the dumb question. Should I bias when replacing tubes in my amp? I am replacing mine with a matched set of JJ's. Any advice appreciated! Thanks!
     
  2. Papa Joe

    Papa Joe Friend of Leo's

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    YEP!!!!
     
  3. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    If it's an unmodded AB568 circuit, it'll have a hum balance adjustment, so all you can do is adjust for least hum, not for an overall "hot" or "cold" bias.

    - Scott
     
  4. Tim Swartz

    Tim Swartz Friend of Leo's

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    Easily remedied by moving a couple wires.
     
  5. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Yep, that mod would be toward the top of my list. ;)

    - Scott
     
  6. rpcruab

    rpcruab TDPRI Member

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    It is an unmodded AB763 Circut.
     
  7. rpcruab

    rpcruab TDPRI Member

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    What should I search for to find this mod?
     
  8. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Perfect! Then you're fine. :cool:

    - Scott
     
  9. Tim Swartz

    Tim Swartz Friend of Leo's

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    If you are basing this statement on the tube chart then it may or may not be an AB763. They used the AB763 tube chart on Super Reverbs until well into 1969, you cannot trust them. Only very early 1968 examples are actually AB763 circuits. Black vertical line on the face plate is an indication of an early 1968 amp, however, the only way to know for sure is to open up the amp.
     
  10. Ben Harmless

    Ben Harmless Friend of Leo's

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    Obligatory "even unplugged amps can kill you, don't open them up if you aren't 100% sure you know what you're doing" statement here.
     
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