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  1. #1
    Member intotubes's Avatar
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    L300 Summits that need a little work

    I stumbled on a pair of L300's and brought them home. They are a bit rough but able to be restored I think. One of the HF drivers was not working, measured 36 ohms DCR. I took the cap off and measured again - 6.1 ohms. Must have been a bit of corrosion. Cleaned off the dust and put them back together and gave a listen. Ugh!
    One MF driver is toast. The other doesn't sound so great either. So I took the cap of the offending driver and found the diaphragm broken in many places. Obviously these have been abused. Clipped to destruction I'd say.
    Anyway here are some pics. Missing the trim pieces on the top. Any repair ideas for that? Grill cloth is filthy and pilled. Not sure it can be resurrected. May have to study the Zilch grill fixing thread. It has the black grills but I s'pose I could use JBL blue. I think that is a stock color for these.
    They have consecutive serial numbers and it looks like the woofers have been reconed. A little sloppy around the dust cap but otherwise looks good.
    The LE85 says 8 ohms but the replacement 'phragms are 16 ohms. Can anyone shed some light on that?
    BTW I found some used drivers for 6 bills a pair. Heck that is the same price as diaphragms. I may pull the trigger on that. All in all I have about a grand banked to restore these. any help, advice, or tips before I do irreversible damage will be appreciated.
    -Mark











    As you can see one is missing the back door. I'll need to somehow fabricate a new one. But they are more than just a door. It supports the MF driver.


  2. #2
    Senior Member Doc Mark's Avatar
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    Hi, Mark,

    Congrats on securing a pair of L300's! As another '300 owner, I think you will love them, once they are restored back into good condition! You've got all the bits, and the rest is time and dollars. As to the midrange diaphragms, you will have to look around a good bit, me thinks, but once you get those LE-85's back to the way they should be, they are very nice, indeed. I might suggest that you check out your crossover, too. Lots of ways to go, there, including going for the whole banana and building what I think are called "CC crossovers" for your new L300's. In any case, if yours were overdriven, it's possible that the crossovers suffered, too. So, check them out, and see how they turn out. Best of luck to you on your project. Restoring your L300's is a very worthy goal, and if you do a bit of looking around in past posts here at LH, you will see some simply stellar work has been done in that regard!! Do yourself a favor and spend the time to seek it here here. You won't be sorry. Take care, and God Bless!

    Every Good Wish,
    Doc
    The only thing that can never be taken away from you, is your honor. Cherish it, in yourself, and in others.

  3. #3
    Senior Member demon's Avatar
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    ...and if you do a bit of looking around in past posts here at LH, you will see some simply stellar work has been done in that regard!! Do yourself a favor and spend the time to seek it here here. You won't be sorry.
    thats a good one:
    http://audioheritage.org/vbulletin/s...ad.php?t=24773
    i think the L3oo are VERY stylish!
    (but i never heard em)
    cheers,
    mikey
    I'm selling a pair of JBL 4435 in Vienna, Austria

  4. #4
    Member intotubes's Avatar
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    I wonder if anyone can address the LE85 diaphragm issue, 16 vs 8 ohms? Will the 16 ohm diaphragms work in my "8 ohm" drivers?

  5. #5
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    Quote Originally Posted by intotubes
    I wonder if anyone can address the LE85 diaphragm issue, 16 vs 8 ohms? Will the 16 ohm diaphragms work in my "8 ohm" drivers?
    - AC impedance is a curve , & one can pick any point on that curve and still be technically accurate in the labelling ( if one wants to be stubborn )


    - I won't bother to spell out in detail JBLs' policy of mislabelling some things while deciding to properly label others, except to say that they did.

    - The following is from an official JBL Customer Service Department publication called ; " Compression Driver Test Specifications " ( circa 1983 ) .
    - ( "DCR = DC Resistance" )


    LE75 , DCR ( min to max ) , 5.4 - 6.6 (ohms) , "Nominal Impedance" = 16
    LE175, DCR ( min to max ) , 5.4 - 6.6 (ohms) , "Nominal Impedance" = 16
    D175 , DCR ( min to max ) , 5.4 - 6.6 (ohms) , "Nominal Impedance" = 16
    175 , DCR ( min to max ) , 5.4 - 6.6 (ohms) , "Nominal Impedance" = 16
    2410, DCR ( min to max ) , 5.4 - 6.6 (ohms) , "Nominal Impedance" = 16
    2420, DCR ( min to max ) , 4.8 - 5.8 (ohms) , "Nominal Impedance" = 16
    275 , DCR ( min to max ) , 4.8 - 5.8 (ohms) , "Nominal Impedance" = 16
    LE85 , DCR ( min to max ) , 4.8 - 5.8 (ohms) , "Nominal Impedance" = 16
    2421B, DCR ( min to max ) , 5.7 - 6.9 (ohms) , "Nominal Impedance" = 16
    2425J, DCR ( min to max ) , 5.7 - 6.9 (ohms) , "Nominal Impedance" = 16

    2421A, DCR ( min to max ) , 3.6 - 4.4 (ohms) , "Nominal Impedance" = 8
    2425H, DCR ( min to max ) , 3.6 - 4.4 (ohms) , "Nominal Impedance" = 8

    - Ideally, when looking for a substitute diaphragm ( because the original is NLA ) one wants to match the impedance curves as closely as possible .
    - Failing having those curves on hand , one should strive to at least get the DCR values as close as possible ( within 1 ohm is nice ) .

    Anyways:

    - The 2421B replacement diaphragm should have a close enough DCR ( @ 6.3 ohms ) to your original 2420 ( le85 ) diaphragms . Plus they are all aluminum and the "weight of the dome & coil" will be correct . The 2410 / LE175 has a lighter weight, dome & coil assembly ( according to the book ) / thus not recommended for substitution into the more powerfull magnetic assemblies of the le85/2420 or 2425 drivers .

    <> cheers

  6. #6
    Member intotubes's Avatar
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    Thank you!

    As always, this is the most technical source of info on the web for JBL/Altec.

    As far as cosmetics, I was thinking of making new trim pieces for the top and then sanding down the veneer in order to finish it together to match. Any ideas of what ind of veneer was used, is it available, can I match it for the trim? What is the finish?
    I'm no cabinet maker so this will be tough for me.

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