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Switchable Cathode Bypass Capacitor for a Tube amp

Discussion in 'General Electronics Discussion' started by Jim Nomad, Jan 22, 2013.

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  1. Jim Nomad

    Jim Nomad

    Nov 26, 2012
    Hi All,
    I am building a simple tube amp using ECC83, I read that the value of the Cathode Bypass Capacitor can have an influence on gain at different frequencies and headroom. Would it be possible to build in a switch so that I can switch between different capicitors and a a consequence produce fully / partially / un - bypassed effect . If so would attached circuit do the job ?
    Many thanks


    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    That should be possible, although I'm in no position to judge the effect.
    I suggest you put the switch on the cathode side of the capacitor.
  3. duke37


    Jan 9, 2011
    The 1uF capacitor will give a turnover frequency of about 100Hz, the 2uF capacitor about 50Hz. I think the gain will rise as the frequency rises and be limited to about 10 times the basic amplifier.

    If you wish to reduce the gain and improve linearity with a constant gain, then you can put a resistor in series with a large capacitor.

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Good point Duke. This would be the most logical way (SOP) to do this. It applies to BJT's and JFETs as well.

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