Biasing a Shiva

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by twangbanger, Jan 3, 2008.


  1. twangbanger

    twangbanger Supporting Member

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    Got a set of =C= EL34's for my Shiva and when I ordered them I told the Vendor that they were for a Shiva and he told me to get them w/ early breakup due to the high plate voltage.installing them I can't get the idle current up past 45ma w/ the bias trim pot.doesn't that seem to cold? Haven't checked for crossover dist yet.I'm using a weber bias right socket set up. Plan on calling Bogner but was interested in opinions from our tube amp guru's here.Thanks for any help.
     
  2. Blue Strat

    Blue Strat Member

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    If anything, 45mA per tube is on the hot side.

    What's the plate voltage?
     
  3. twangbanger

    twangbanger Supporting Member

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    Thanks for the quick response Mike! the plate voltage is 521v.
     
  4. frankencat

    frankencat Gold Supporting Member

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    That does seem pretty hot for EL34's at 521VDC. I wouldn't go much past 35ma at that voltage. FWIW, I called Bogner once to ask them how they bias and they told me they use a scope and that I would not be able to bias it correctly without one. :rolleyes: The first Shiva I bought was biased way cold and even cranking the trimmer all the way down only got it into the low-adequate range for a pair of SED 6L6's.
     
  5. Blue Strat

    Blue Strat Member

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    34mA would be 70% which is too high.

    Low 30s would be more like it. At 45mA you're almost at 100% plate dissipation which is a VERY bad idea.
     
  6. twangbanger

    twangbanger Supporting Member

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    Thanks so much for the info,I should have done the math! Always pays to ask, Especially on this forum.
     

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