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Thread: Advice from ampman Premier guitar mag

  1. #1
    Alf
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    Advice from ampman Premier guitar mag

    In an item about removing two powertubes to lower your outputpower Ampman ( from Premier Guitar magazine) he advised to also halve your impedance. e.g. from 8 0hm with 4 powertubes to 4 ohms with 2 powertubes.
    Well I thought it was just the other way round ! If you have an 8 ohm cabinet connected with four valves you should use an 16 ohm cab with 2 valves ??

    Am I wrong ? Who can lighten this up ?

    Alf
    Last edited by Alf; 04-23-2014 at 02:33 PM. Reason: Not complete

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    Supporting Member Chuck H's Avatar
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    To be more specific than your post implies, you want the your impedance switch set to 4 ohms when you remove two power tubes if it is normally set to 8 ohms with all four. The implication being that you should play the amp into an 8 ohm load with the amps impedance switch set to four ohms, effectively doubling the speaker load impedance. The article probably did specify this.

    To be clear, if you didn't have an impedance switch and your amp wants an impedance of 8 ohms, if you pull two power tubes you want to plug into a 16 ohm load, effectively doubling the speaker load impedance. This is probably what you were thinking.
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    Alf
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    Quote Originally Posted by Chuck H View Post
    To be clear, if you didn't have an impedance switch and your amp wants an impedance of 8 ohms, if you pull two power tubes you want to plug into a 16 ohm load, effectively doubling the speaker load impedance. This is probably what you were thinking.
    So I was right . I am asking this because I have a Fender twin copy with a Mercury Magnetics OT with only 4 ohm out and use it with only two tubes in an 8 ohm cabinet.
    The amp doesn't have an impedance switch.

  4. #4
    g1
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    Yes, that will work for you because you have no impedance selector.
    What Ampman said was to halve the impedance setting, not the cabinet impedance. Unfortunately he didn't word it well. "change the output impedance selection to reduce the speaker load by half": by mismatching with the switch, you are reducing the effective load, not the actual load.
    So you were both right, just for different situations, like Chuck explained.
    "there's another kind of party lights that I can't stand to see,
    when there's a man in that patrol car and he don't wanna party with me"

  5. #5
    Alf
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    Thanks for clearing this up , so it was another example how language can distort things sometimes.
    g1 likes this.

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