Technical Electrical Question: BML 105070 stereo radio in a 1959 Triumph TR3A? | FerrariChat
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Technical Electrical Question: BML 105070 stereo radio in a 1959 Triumph TR3A?

Discussion in 'British' started by NeuroBeaker, Apr 25, 2011.

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  1. NeuroBeaker

    NeuroBeaker Advising Moderator
    Moderator

    Oct 1, 2008
    40,044
    Huntsville, AL., USA
    Full Name:
    Andrew
    #1 NeuroBeaker, Apr 25, 2011
    My dad bought a BLM 105070 stereo radio to install in his 1959 Triumph TR3A. This radio is original equipment from Jaguar Rover Triumph Inc and the installation instructions show that it was used for MGB, Triumph TR7, TR8 and Jaguar XJS, XJ6 & XJ12. Does anyone know if he can safely hook this up to a Dual Voice Coil speaker with 4 ohm impedance?

    We believe that 4 ohms is the standard for automotive speakers since at least the late 70's - and probably has been for longer than that, but we're not sure. If the radio needs 8 ohms it'll be damaged if connected to 4 ohm speakers. So we need to confirm before attempting the install.

    Thanks very much in advance. :)

    All the best,
    Andrew.
     
  2. Miltonian

    Miltonian F1 Veteran

    Dec 11, 2002
    5,966
    Milton, Wash.
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    Jeff B.
    #2 Miltonian, Apr 25, 2011
    A 1959 Triumph TR-3 has a positive-earth electrical system, which is probably not compatible with your stereo.
     
  3. NeuroBeaker

    NeuroBeaker Advising Moderator
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    Oct 1, 2008
    40,044
    Huntsville, AL., USA
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    Andrew
    #3 NeuroBeaker, Apr 25, 2011
    I just called Dad to ask him about that and it turns out I was lacking some critical information... he has previously changed the car's electronics to a negative earth.

    He was phoning electronics shops for information while I was putting this thread up here and he just sent me this reply:

    Issue Closed: I talked to a tech adviser at {business removed}. He had access to old vehicle specs and confirmed that TR7/TR8 had 4 Ohm speakers! Since the installation guide for my OEM stereo says it works with the existing speakers in a TR7/TR8, it must be compatible with 4 Ohm speakers. I'm going to install a 5"x7" DVC Speaker so I retain the original single speaker configuration that was an option of the day :)​


    Thanks very much for getting back to me Jeff, it is appreciated. :cool:

    All the best,
    Andrew.
     
  4. AugustWest

    AugustWest Karting

    Mar 1, 2011
    57
    Los Angeles
    #4 AugustWest, Apr 26, 2011
    If your speakers actually are dual voice coil (though I suspect they're co-axial), and each VC is four ohm, then you have either a two-ohm total load (if the VCs are wired in parallel), or eight ohm (if they're wired in series). "If in doubt, get the meter out," meaning it's best to put a meter on speaker leads to read for resistance before testing things merely by turning the system on (and potentially losing the magic smoke contained therein). A four ohm voice-coil will show 3.7 ohms of resistance.
     
  5. AugustWest

    AugustWest Karting

    Mar 1, 2011
    57
    Los Angeles
    #5 AugustWest, Apr 26, 2011
    The more I've thought about this - the more I'm doubtful your father's speakers are dual voice-coil (which is often seen in subwoofers, but almost never in anything smaller than 8" in diameter). The only real reason for dual voice coils is it makes mixing amps/speakers easier (sometimes) by offering a range of loads to show to an amplifier (especially when using more than one speaker on a channel (or bridged amp))... ....this is helpful with subwoofers, but pointless on anything playing above 90hz.

    Do the speakers have four terminals - indicating dual voice coils; or do they have two terminals (a single voice coil). My guess is they have two terminals (single voice coil), but they are co-axial (meaning there's a tweeter mounted to the frame along with the mid-woofer)...

    Get that meter out before reconnecting that positive battery cable!
     

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