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A question for the tube heads

Discussion in 'Amps [BG]' started by Jerry Ziarko, Dec 30, 2013.

  1. Jerry Ziarko

    Jerry Ziarko Supporting Member

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    I am picking up a tube head for the first time in decades. The ohm switch on the back is the usual 8, 4, 2 ohms. How would I set it to work with my Epifani 310? It is a 5.3 ohm cabinet. Thanks for any help...
  2. B-string

    B-string Supporting Member

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    It is really open to a consensus of opinion but IMO I would set it at 8 ohms, 4 ohms would most likely not cause any trouble.
  3. beans-on-toast

    beans-on-toast

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    I'll reiterate the same thing.

    Either way, you have an impedance mismatch. How well an amp deals with a mismatched impedance depends on the design of the amp.

    The general rule of thumb with a tube amps is that it is better to connect a lower impedance than a higher impedance cabinet. So following that rule, set the amp's output impedance to 8Ω. This mismatch will mean that the tubes will be pushed a little harder. Having said that, 5.3Ω is closer to 4Ω than to 8Ω. Running the amp at 4Ω will work as well. Try both and see if you like the sound of one configuration over the other.

    It would be worth asking Epifani. They must have feedback from users on this issue and know what works best with their cabs.
  4. Kmonk

    Kmonk

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    Disclosures:
    Endorsing Artist: Fender and Spector, Ampeg, Curt Mangan Strings
    I agree. 8 ohms would be the safest.
  5. dincz

    dincz

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    Percentage-wise, the mismatch is the same either way - the load is 33% high or 33% low. But I agree that a slightly low load imedance is preferable to high, i.e. set amp to 8 ohms to drive a 5.3 ohm load.
  6. StuartV

    StuartV Out of GAS!! Supporting Member

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    Or check with the amp manufacturer....?
  7. AstroSonic

    AstroSonic Supporting Member

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    8, 5.3, 4. These are all 'nominal' impedances. The impedance varies substantially with frequency, typically rising well above the nominal impedance below around 100Hz and above about 1kHz. In this case, the 8 ohm setting would likely have better power delivery and control through the low end, where power delivery and control are needed most. Do not get stuck on this. It is perfectly permissible to try neighboring impedance settings (like 8 and 4 in this case), listen to the sound and choose the one that works the best.
  8. beans-on-toast

    beans-on-toast

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    Yes percentage wise you are correct.

    In terms of non linear impedance 5.3 is 1.3 ohms away from 4 while it is 2.7 ohms away from 8. A 5.3 Ω cab might have an average DC resistance of 3.7 ohms. That's what I meant when I said closer to 4.

    I think that trying and listening is the best thing to do. Setting it at eight ohms is the safest thing to do.

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