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12ax7 pin 8...grounded?

Discussion in 'Shock Brother's DIY Amps' started by alias23k, Aug 14, 2009.

  1. alias23k

    alias23k Tele-Meister

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    i have a shematic that does this with a 68k resistor. all other schems that i've read pins 3 and 8 are connected then goes to the output stage. I've read this increases gain but offsets current values.

    Any input on this? Thanks.
     
  2. celeste

    celeste Friend of Leo's

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    Pins 3 and 8 are the cathodes of the 12a?7 family. In a grounded cathode amp stage, the resistor to ground from the cathode sets the bias point, this effects everything about the AC transfer of the stage.
     
  3. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    What schematic?

    What do you mean when you say that "all" other schematics show both cathodes tied together and going to the output stage?

    You could tie cathodes together, but they're not "all" done this way by any means.

    Like celeste mentions most amps are used in a grounded cathode setup and it sets the tube's bias. A bypass cap is a sort of negative feedback circuit there.

    Maybe the schematic you have can help answer your question better...
     
  4. alias23k

    alias23k Tele-Meister

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    thanks for the replies guys. i posting a new thread where you can read the finished layout. please disect and critique. i'll post more info there.
     
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