Tone of Fixed vs. Cathode Bias

Discussion in 'Amp Central Station' started by bobbyk, Feb 20, 2012.

  1. bobbyk

    bobbyk TDPRI Member

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    Okay, take the same 2 x 6L6 amp. Is there a noticeable difference in the tone if the amp had fixed bias as opposed to cathode bias? Noticeable enough that doing a fixed/cathode mod would be worth the effort?

    Thanks in advance.
     
  2. celeste

    celeste Friend of Leo's

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    There is still a lot of room for other parts of the circuit to have large effects on the outcome. The presence and size of the cathode bypass cap has a major effect on the feel or a cathode biased output stage,
     
  3. printer2

    printer2 Poster Extraordinaire

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    Put a 1000uF cap across the cathode resistor to get an idea on the difference. Tried it on one amp I have and while I can hear a subtle difference when I switch it in it does not change the sound much. As celeste says, other parts may determine how much of an effect it has. I have a feeling it would not make much difference with my combination. Not going by experience but I have the feeling it would be more noticeable the higher in power the amp.
     
  4. celeste

    celeste Friend of Leo's

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    Don't forget, Vak changes switching between the two, unless you turn the B+ on the fixed configuration by an amount equal to the bias voltage of the cathode biased configuration.
     
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