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Thread: What is this inductor value

  1. #1
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 1,250
    I'm Chris.

    Default What is this inductor value

    This may be asking the impossible, but you don't know till you try

    I have a pair of these inductors taken from a vintage pair of Rogers speakers. I have no way to measure their values - all I have is that the resistance is about 0.5 ohms, the copper winding about 1.4mm and the weight of each is 450g. The central square former is plastic/ Bakelite.

    Would anybody like to hazard a guess at the value.

    If its totally impossible to guess, please say so. This will stop me waiting on answers.

    Thanks

    Chris
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  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 6,089
    I'm Alan.

    Default

    Could make a stab at it if the number of turns were known.

    Or 2 seconds to read the value on my LCR meter.
    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  3. #3
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,881
    I'm Lawrence.

    Default

    Or tell us which model they're from and we might be able to work it out from available schematics.

    Sent from my BKL-L09 using Tapatalk

  4. #4
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 1,250
    I'm Chris.

    Default

    Alan
    I didn't know there was a simple meter that could make this measurement. Everything I read suggested I needed an oscilloscope Found LCR meter at less than £25 so its on my borthday list.

    Lawrence
    Inspired by your post I went out to the shed to see if I could make out the model number on the old stripped Radford cabinets I stored there. And then a magic moment - when I found the crossover circuit diagram on a metal plate. The main driver was a KEF B139 with inductor of value 2mH.

    So, mystery solved. Thanks for your help.
    Source
    SW1X Universal Music Server UMS I Signature with Power Supply Unit PSU I Signature
    SW1X USB II
    SW1X DAC III Special
    Audiolab 6000 CDT transport
    Amps
    Pre amps -- Hi fi Collective twin mono ladder stepped attenuator, with Charcroft Z-foil and silver wired. And First Watt B1 active no gain buffer.
    Power amps -- Welborne 45 SET monoblocks 1.8W / Decware Taboo 6W / Elekit 300B TU-8600SVK plus further improved components 9W / ICE Power 1000W
    Speakers
    Highly modified Endorphin P17 open baffle speakers containing both vintage and modern alnico drivers and paper cones. All silver wired - 8" Cube Audio FC8 full range drivers and vintage 15" Altec VOTT 416 bass drivers. All sat on Townsend Audio Podium seismic isolation platforms.
    BK Electronics XLS400FF Sub.
    Cabling
    Silver mains cables, interconnects and speaker cables by SW1X
    Headphones
    HRT HeadStreamer and SennHeiser HD650 headphones

  5. #5
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,881
    I'm Lawrence.

    Default

    Great news. I wonder if that's the same inductor value as in the B139 filter in the Kef Concerto crossover you can get from Falcon.

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  6. #6
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,881
    I'm Lawrence.

    Default

    It seems the Concerto also had a 2mH inductor as I suspected. Interestingly there was a later concerto crossover that used a 4mH inductor.

    https://www.falconacoustics.co.uk/ke...r-upgrade.html


    Sent from my BKL-L09 using Tapatalk

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