What do you know about Jensen Concert series?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers T' started by mbratch, Jul 20, 2008.

  1. mbratch

    mbratch Member

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    I have two:

    EM1250 C8139-8
    EM1220 C8138-4

    They're gray, ceramic, with nice bell covers. Dated 1966 and 1967.

    I have found very little info from Googling. I only found one statement that the EM1220 might be a 100watt speaker (?). I would have guessed 20 myself, but what do I know? ;) I'm also supposing the dash numbers are impedance ratings?
     
  2. slider313

    slider313 Silver Supporting Member

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    Most Vibrantos/EM Series Jensens were higher wattage C12P's.If you look at the voice coil size it should be 1.5".Some cones were different in the amount of ribs used and different coils were higher temperature. I believe the 1220 was a bass speaker and should have more ribs for a brighter and tighter attack.The 1250 was,I believe,a guitar speaker and should have less ribs than the 1220 and should be a 25 watt speaker.Do the cones have the same amount of ribs and is the voice coil the same size? What are the 301.......codes on the cones?
     
  3. mbratch

    mbratch Member

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    I'll check those things when I open it back up.

    What about impedance? Are these 8 and 4 ohms, respectively?
     
  4. slider313

    slider313 Silver Supporting Member

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    I've never seen a 4 ohm Jensen,only 8 and 16.I don't think the -4 or -8 are ohms.
     
  5. mbratch

    mbratch Member

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    Thanks slider.

    Which leads me back to one of the questions: how to know what the impedances of these speakers are.
     
  6. slider313

    slider313 Silver Supporting Member

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    Get a multimeter, set it to ohms and take a reading.The DC resistance will always be less than the ohm rating; 8 ohms may read 7.2 ohms.
     
  7. mbratch

    mbratch Member

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    Thanks slider. I had tried that measurement, but my mongoloid RadioShack meter doesn't seem to settle on a value when attempting that measurement.
     
  8. mbratch

    mbratch Member

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    Got some info from an audiophile forum:

    EM-1220: 28oz mag, 8 ohm, 1.5" VC, for Bass Guitar and String Bass
    EM-1250: 28oz mag, 8 ohm, 1.5" VC, for Guitar, Combo Organ and Accordian

    As you said slider. Probably a cone difference for different apps...
     
  9. mbratch

    mbratch Member

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    I haven't taken the speakers out yet, but while I was in the back of the cab tonight, I got the 301 codes:

    3012B16W5
    3012B16W6? (it might actually end if 5, and is smudged?)

    I can see the ribs from the back side. They both appear to have 10 ribs.

    Don't know yet about voice coil.

    I did measure the resistance. The 1220 was 6.something, the other (1250) was a little over 8.
     
  10. slider313

    slider313 Silver Supporting Member

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    They could be very similar with one having a higher temperature voice coil. Another thing to check would be the size of the dust cap.
     
  11. mbratch

    mbratch Member

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    OK finally took them out to look at them.

    The cones look identical. Even their age (same amount of dust accumulated along the bottom). They've both been in the cabinet awhile. And both have the same dust cap diameter, 1-3/4".

    You're probably right about the voice coil difference.
     

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