4x10 ohm questions

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

  1. MikeNiteRail

    MikeNiteRail Member

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    My amp is set up to take a 4ohm load. How would I wire a 4x10 with 6l6s to take 4ohm? I have two 8ohm speakers already and could get two of whatever ohmage to make the correct load. I just don't know the best way to wire.

    What if I switched to 6v6 tubes, what would I do then?
     
  2. tlpruitt

    tlpruitt Member

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    I don't believe it is possible to wire four 8 ohm speakers to create a 4 ohm load.

    If you wire four 8 ohm speakers in parallel you would get a 2 ohm load. If you wire four 8 ohm speakers in series/parallel you would get an 8 ohm load.

    -Tim
     
  3. tmac

    tmac Goldmember Gold Supporting Member

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    I believe to make it come out to four ohms you'd need four 16 ohm speakers in parallel to make it 4 ohms (or four 4 ohm speakers wired in series parallel). For 16 ohm speakers you could wire it like a Fender Super Reverb to make a total load of four ohms (instead of the four 8 ohm speakers to make 2 ohms). This way you'd have equal power going to each speaker.
    http://schematicheaven.com/fenderamps/super_reverb_ab763_schem.pdf
     
  4. Blue Strat

    Blue Strat Member

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    +1.
     
  5. MikeNiteRail

    MikeNiteRail Member

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    Thanks! I have a switch to run the amp at 4ohm or 8ohm. Does that make a difference with anything? I thought the 8ohm was for 6v6 tubes.
     
  6. tlpruitt

    tlpruitt Member

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    If the amp has a switch to go choose a 4 or 8 ohm output then set the switch to 8 ohms and wire four 8 ohm speakers in series/parallel and you would get an 8 ohm load and you are set.

    The switch selects different taps on the secondary of the output transformer. As long as you are using the output tubes that the amp and the output transformer were designed to be used with then the 4 and 8 ohm references on the output switch should be accurate.
     
  7. jdh

    jdh Supporting Member

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    MikeNiteRail,

    Assuming you could get 6V6 tubes that will survive the higher voltage seen by the 6L6's, The taps on the output transformer will now be 8 ohms and 16 ohms.

    Dennis
     
  8. MikeNiteRail

    MikeNiteRail Member

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    Thanks again for all the info, guys.
     
  9. SatelliteAmps

    SatelliteAmps Member

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    How do you figure that without knowing the amplifier? Chances are the taps will remain the same.
     
  10. GearHeadFred

    GearHeadFred Member

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    jdh is right.. 6V6s have about double the plate resistance of 6L6s, so to stay balanced, you need to double the speaker impedance.
     
  11. SatelliteAmps

    SatelliteAmps Member

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    Without knowing the amp and output transformer, I would disagree. Plate resistance is part of the picture but so is the transformer. Plate resistance has quite a range for both tube types without determining specific load matching.
     
  12. jdh

    jdh Supporting Member

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    Let's assume MikeNiteRail's amp is, to a first approximation, designed properly. Connecting a 4 ohm speaker to the 4 ohm secondary tap will reflect 4K ohms to the primary. This impedance ratio of 1000:1 provides the 4K ohm loading the 6L6's want to see. The load on the secondary determines the impedance reflected to the primary. It is true that plate resistance does vary, but as a beginning design point a pair of 6L6's needs a 4K load, and a pair of 6V6's needs double that. Connecting an 8 ohm speaker to the 4 ohm secondary tap will reflect 8K ohms to the primary. The transformer's impedance ratio does not change, is still 1000:1, and this is a good starting point for a pair of 6V6's.

    Dennis
     
  13. SatelliteAmps

    SatelliteAmps Member

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    I agree for properly designed amps.

    Maybe I'm not explaining myself very well.

    There are some amps out there with poorly designed (or not even considered) transformers, where this is not as accurate of an example. There are also some amps out there that were intended for a compromise of being able to use a variety of tube types without having to adjust the impedance (or in some cases even the bias). There are some with outputs designed purely by wattage without regard to even a turns ratio, plate impedance, tube type, or even really application.

    I just don't really like blanket statements of automatically adjusting for things that may not need to be adjusted for. Just my opinion though.
     

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