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Quick tube pulling question (100w -> 50w)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by somedude, Nov 7, 2005.

  1. somedude

    somedude Member

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    I'm pulling a pair of tubes out of a 100w head to get the headroom down.....I just need to confirm that when pulled speaker outs on the back halve in impedance, ie;

    8ohm becomes 4ohm



    or is it



    8ohm becomes 16ohm


    I'm almost certian it's the former, but I'd like to confirm things before I turn it on.
     
  2. TubeAmpNut

    TubeAmpNut Member

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    8 Ohms becomes 8 Ohms. The transformer turns ratio doesn't change...

    If you want to load a pair of tubes the same as what a quad would see, use the 4 Ohm selector with an 8 Ohm cab, etc.

    You don't, however, need to reset your impedence switch. Kevin O'Conner explains it well.

    http://www.londonpower.com/faq.htm

    BK
     
  3. bob-i

    bob-i Member

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    BK-Amps is correct, you don't HAVE to change the impedance switch. Personally I've done this a few times, usually because a power tube died in the middle of a gig and I removed it and it's partner to balance the output. The results are not what you'd expect. Typically I found that the amps was almost as loud but the tone was weaker, not as much highs especally.

    Removing the 2 tubes to get 50 watts will lower the max volume about 3Db. To my ears this is almost not noticable. I've found that lowering the impedance, I.E. switch from 8 to 4 ohms, brings back some of the lost tone, but overall I've found that amps tend to sound best when they're operated as they're designed.
     
  4. somedude

    somedude Member

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    Thanks guys.

    Yeah, I don't find a whole lot of difference in volume between 50w and 100w amps anyway.....it's more of an experiment to see what changes it makes to the tone, and whether I like those changes or not.

    So far it seems darker and a little more spongy on the attack, but I haven't had the chance to light the amp upto gig volume yet to see what I think of it.

    Anyway, cheers. :)
     
  5. hasserl

    hasserl Member

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    I think the difference in power mostly shows up in a band situation. When playing by yourself in your bedroom or garage you won't hardly notice it. But play with drums and bass, and especially with another guitar, and the difference becomes more apparant. It might be just the amount of volume you needed to scrub off to not be too loud to everyone else. An attenuator set for minimal attenuation might accomplish the same thing. But that costs more. This way is free.
     
  6. TheAmpNerd

    TheAmpNerd Member

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    Kevin is a good guy. However, it is always difficult
    to hunt things down in his books. It's funny that
    he listed a link to TUT4, which isn't even out yet.

    bob-i, that makse sense too. With the right load back
    it should sound similar again. 2 tube @ 4 ohms.
    If it was 4 tubes @ 8 ohms ideal then you might
    get a similar mismatched tone using 4 tubes @16 ohms.
    Meaning it might be similar to the 2tubes at 8 ohms.
     

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