What voltage does a Vibro Champ's 12ax7 like to see ...

Discussion in 'Amp Tech Center' started by trouserpress, May 6, 2021.

  1. trouserpress

    trouserpress Tele-Holic

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    .. for example to help a good sounding amp sound better?
    Someone on another forum said there shouldn’t be more than 200V at V1. At my Vibro Champ’s V1 I read 220V (spec=205V) at pin 1 and 215 (spec=200V).

    Is it worth struggling with the dropping resistors? Lately I brought the bias resistor from 570R (->13,5 Watts) down to 470R (stock -> 14,3 Watts). Soundwise that change wasn’t altogether good: Seems I traded „fenderishness for mellowishness“ (oh dear - forgive me).

    Any thoughts?
     
  2. jimgchord

    jimgchord Tele-Afflicted

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    20 volts wont make much difference. I prefer to change the cathode and load resistors if a v1 bias change is needed rather than mess with the dropping resistors.plot the load lines to see where you need to go.
     
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  3. trouserpress

    trouserpress Tele-Holic

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    Thanks Jim, that's about where I was gravitating to. I think about it some more and will probably swap the cathode resistor and the plate load resistors for slightly bigger ones.
     
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