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Thread: Removing two of four power tubes. Can it be done affectively to cut wattage?

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    Question Removing two of four power tubes. Can it be done affectively to cut wattage?

    Hello Everyone
    I am brand new to this site. I have heard of but never witnessed players being able to remove 2 of 4 power tubes to lower the wattage of their amp.

    I know the remaining tubes would have to be working opposite, one for each side of the wave.

    1. Are there certain amps that this can be done with easily?
    2. Is it as simple as re-biasing the remaining 2 tubes or much more involved?
    3. Is it not advised and why?



    I just picked up a Hughes & Kettner Statesman Quad EL84 40 watt combo and wondered if the wattage could be lowered by doing this. I know they make a duel EL84 version too coming in at 20 watt rms. The new amp sounds great as is and is more versatile than all my other amps, but it is really loud like my old Marshall.

    I could not find this question anywhere else on the site. Also, I am not circuit savy.

    I am thinking this could be a pretty good subject for newbies. Thanks for any info!

    Stew

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    Lifetime Member Enzo's Avatar
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    It is done all the time. Bias rarely needs much change,, but you do need to adjust the output impedance. In other words your 16 ohm cab now plugs into the 8 ohm output.

    You have to be aware some amps will not work like that. Peavey Valve King amps for example run the power tube heaters in series, so pull any and they ALL go dark. Same with Classic 30.

    But you said the magic word: loud.


    Power and loudness are not the same thing. Cut power in half and it is only 3db less loud. NOT half as loud, just 3db.

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    Quote Originally Posted by Enzo View Post
    It is done all the time. Bias rarely needs much change,,.
    ...if it's a fixed bias amp. A guy ran a 4xEL84 cathode-biased Laney on 2 tubes for 3 years. I measured 18w/tube in idle. The logo on the tubes turned all black, but they still sounded great. Those JJ EL84's are tough little beasts 👍

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    Lifetime Member Enzo's Avatar
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    That is true, cathode biased power tubes may not like it. Thank you.

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    Thanks everyone for the great replies!

    Quote Originally Posted by Enzo View Post
    That is true, cathode biased power tubes may not like it. Thank you.
    I just want to thank everyone for the great replies and in record time!

    Stew

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    The topic was discussed a few days ago, see https://music-electronics-forum.com/...ad.php?t=47484 for more debate / analysis.
    Basically, to me it seems pretty pointless, as it may mess up the amp's tone and response without much noticeable reduction of the max SPL it creates.

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    Last edited by pdf64; 10-23-2018 at 10:35 AM.

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