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Thread: Replacing E120 aluminium dustcap questions

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    Replacing E120 aluminium dustcap questions

    I intend to replace aluminium dustcaps on E120 with paper dustcaps.

    What kind of glue did JBL use on these? Can the dustcap be removed after heating?

    Any advice on the subject is appreciated

    /Mårten

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    Senior Member edgewound's Avatar
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    Quote Originally Posted by more10 View Post
    I intend to replace aluminium dustcaps on E120 with paper dustcaps.

    What kind of glue did JBL use on these? Can the dustcap be removed after heating?

    Any advice on the subject is appreciated

    /Mårten
    The glue used for the E120 dust cap could be either black Bostik or Loctite Black Max. It takes a bit of mental and manual creativity to remove either dustcap glue. I'm afraid you're on your own because the only determiner of success is your own manual talents and experience.

    Good luck!!
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

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    Thanks Edgewound!

    The Loctite seems to be cyanoacrylate with rubber. Acetone can be used to debond cyanoacrylate according to wikipedia. Ill try with an ugly driver first.

    Another option would be to paint the dome with aquaplas or something similar.

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    Senior Member maxwedge's Avatar
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    I never did like the look of the chrome dome seen through the grill of a Twin Reverb!

    Edit: Not trying to spam. What is the reason for changing?

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    The reason for changing is to see if it is possible to make them sound any better. I am using them as midranges. There is a rise above 1k that I believe is because of the aluminium dome.

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    Check this so You know what to expect

    http://www.audioheritage.org/vbullet...=e140+dust+cap

    Before You cut away the aluminium dome You can try to damp it by painting it with undercoating or something similar. What can You spoil?

    Try to lend some measuring device, such as a Behringer DEQ2496 and a mike.

    I would like to understand what causes the rise starting at 1 kHz.

    Ruediger

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    Senior Member ivica's Avatar
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    Quote Originally Posted by more10 View Post
    The reason for changing is to see if it is possible to make them sound any better. I am using them as midranges. There is a rise above 1k that I believe is because of the aluminium dome.
    Some kid of rise response in frequency response is expectable (over 1kHz,), concerning the directivity characteristics of 12"-inch drivers. Such behavior is visible on:
    http://www.audioheritage.org/vbullet...l=1#post148781

    and nicely explained in Altec Lancing Technical Letter no.237:

    http://alteclansingunofficial.nlenet...ers/TL_237.pdf


    expectable 6dB/octave rise in 'on-axis' response is well explained in above TNL-237,
    but response decline with the angular off-axis response too, so some work on crossover network can be helpful.

    I expect that total amount of radiated audio energy remains almost constant up to 2~4kHz.
    "Painting" or exchanging dist cup I think would not give too much in 'flattening" the on-axis response,
    so removing aluminum dust-cup can produce more trouble.

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    My memory is probably somewhat faded after all these years, but I seem to remember that the lightweight curvilinear cone had some breakup around that frequency. Try sprinkling some talcum powder on the cone and sweep around that frequency.
    Harvey "Hifi" Gerst
    ("Hifi" was my nickname at JBL.)

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    Thanks for all advice.

    I very much like Harveys suggestion, I will certainly try it.

    Very instructive thread Reudiger!

    Before removing the dustcap I will try to dampen it with some kind of rubber glue. Maybe stiffening the cone as well. I have a few beaten drivers which I can experiment on.

    /Mårten

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    Senior Member 57BELAIRE's Avatar
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    [QUOTE=maxwedge;329742]I never did like the look of the chrome dome seen through the grill of a Twin Reverb!

    How's this?
    Attached Images Attached Images  
    OPUS POCUS

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    Senior Member maxwedge's Avatar
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    Quote Originally Posted by maxwedge View Post
    I never did like the look of the chrome dome seen through the grill of a Twin Reverb!
    Quote Originally Posted by 57BELAIRE View Post

    How's this?
    Personal preference sir?

    I have a 61 Bandmaster too. That cabinet looks smaller that the usual Bandmaster cab, is it original?

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    Senior Member 57BELAIRE's Avatar
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    that's a 1960 Showman 12, serial #00028 . I bought it used for $250 in '62 at Ace Music in Miami.

    to me that centerdome was the coolest thing ever...it let everyone know you were JBL equipped!
    OPUS POCUS

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    And that's the main reason I went with the aluminum dome on the D140F: You could see they were JBL's from a mile away.
    Harvey "Hifi" Gerst
    ("Hifi" was my nickname at JBL.)

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    Senior Member maxwedge's Avatar
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    Ok Ok, I love em too!
    I loaded an Ampeg V4 with 4 E120s for the same reason, way back when.

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