Plate dissipation vs. Power output at speaker

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Nekle, Sep 18, 2005.

  1. Nekle

    Nekle Member

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    How do these differ? Is the power consumed at the plates different from the power as it comes out of the speaker? How do any losses occur? Sorry if this has been asked before.
     
  2. Nekle

    Nekle Member

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    thank you old tele man.
    Is 90% then a good "general rule of thumb" type thing to use? And is that with matched loads only?

    What about when the OT primary impedance is coupled to a 16 ohm secondary and you tag an 8ohm speaker on it? this will reflect back to the primary half it's original impedance (correct?). So if the tubes originally needed a plate to plate resistance of say, 6600 ohms, they would now be seeing 3300 ohms meaning more current would be travelling through both sides of the OT. Since the plate voltages have stayed the same does this mean that we are increasing our power output at the speaker simply by mismatching the loads?
    Thank you for your help.
     
  3. Blue Strat

    Blue Strat Member

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    Mismatching speaker loads reduces power to the load. There's no way around this.
     
  4. Nekle

    Nekle Member

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    thanks blue strat. I don't think I'll ever understand this stuff:(
     
  5. Wakarusa

    Wakarusa Member

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    Try this: Electron-Tube Circuits

    Go to Chapter 9 (Untuned Power Amplifiers). Excellent description of exactly how power to the load (vs. dissipated in the plates) is worked out. Not nearly as technically dense as RDH4.

    Edit: Look at figure 9-2. It's a graph of the equation right above it. This is for a triode, but still gets the idea across. The salient point is that maximum power transfer is achieved only when the plate and load resistance is equal.
     
  6. Nekle

    Nekle Member

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    Thank you for that Wakarusa!
     
  7. StompBoxBlues

    StompBoxBlues Member

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    I know that the power output transformer works, that as the current collapses on the negative going side of the wave, it induces a postive going on the other side.

    This is why there is no "cheating" the trafo, getting something for nothing...it is only optimal when the impedance matches for effective transfer.

    BUT...I had a big question rolling around in my empty brain for a while now, trying to decide and theorize on what the answer could be...

    I was wondering this, does it make any difference which of the settings you choose while they match?

    But this I mean, if you have a selectable impedance cabinet AND amp, go extreme and say you can either set both cabinet and amp to 4 ohm impedance, or 16 ohm impedance.

    Is one of those inherently a little better than the other, or is it exactly the same? Do the speakers work any better/worse/harder or the amp when it is one or the other?
     
  8. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    They'll sound different due to differing damping factors.

    Do a search for "speaker AND damping" for the 411.
     
  9. StompBoxBlues

    StompBoxBlues Member

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    Thanks for the tip. Interesting stuff.
     
  10. Nekle

    Nekle Member

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    Yes, thank you all very much for helping with this:)
    I'd like to try and build one of my own some day but I'm not even close to being ready for it yet. Slowly though I'm hoping to get there!
     

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