How to identify speaker terminals (Ohms)

Discussion in 'Hi-Fi and General Audio' started by PSXmad2, May 12, 2007.

  1. PSXmad2

    PSXmad2

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    Is the a way to identify, using a multi meter, which of the positive output terminals are 4 ohms and which are 8 ohms. Is this done powered up or off ? Laymans instructions wanted.
    Thanks
    Tony
     
    Last edited by a moderator: May 12, 2007
    PSXmad2, May 12, 2007
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  2. PSXmad2

    zanash

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    normally they will be marked on the cabinet ...

    if you have a multimeter ...put the black probe to the black terminal and the red to red, set the unit to read ohms or continuity read off and make a note ...repeat for all terminal sets

    you should have a low set and a high set .....

    now if you talking about the amp .....

    whip off the base cover and look to see which set has the resistor from plus to negative ....or with the amp off test the same way [with cables removed ] as the speakers ....

    though normal convention seems to be that the 8 ohm terminal is on the out side of the negative .....[well on my valve amp]
     
    zanash, May 13, 2007
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  3. PSXmad2

    PSXmad2

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    Thanks Pete, Yes i`m talking about the amp terminals I did a quick measure and in ohms one measures 1.0 and the other measures 1.5, which is which ?. Or if I look inside, which is which the one with the resistor 4 ohms or 8 ohms.
    Thanks
    Tony
     
    PSXmad2, May 13, 2007
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  4. PSXmad2

    zanash

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    the resistor is to the 8ohm terminal .....

    only a small difference in measured ohms ....so that is not conclusive

    ..whats the amp again ?
     
    zanash, May 13, 2007
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  5. PSXmad2

    PSXmad2

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    Its a Phil Ramsey built 300B set, I will take the bottom off and have a look.
     
    PSXmad2, May 13, 2007
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  6. PSXmad2

    RobHolt Moderator

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    Are we talking 8 and 4 Ohm transformer taps here?

    If so, the higher figure of 1.5 ohms is the one to use for the 8 Ohm speakers. The higher resistance on the 8 ohm tap results in more turns of copper wire used on the secondary of the output transformer - now't to do with resistors.

    I don't know this amp but if there are any resistors across the output they are likely present to kill any transformer ringing or instability - you may see them in series with small caps.
     
    RobHolt, May 13, 2007
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  7. PSXmad2

    PSXmad2

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    Thanks for all the info, I`ve had a look inside and can`t see any resistors accross the outputs so have put the cable in the outputs with the highest resistance. all seems to be working well.
    ATB
    Tony
     
    PSXmad2, May 13, 2007
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