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more10
02-26-2012, 10:28 PM
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

edgewound
02-27-2012, 12:05 AM
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!!

more10
02-27-2012, 03:32 PM
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.

maxwedge
03-01-2012, 01:17 PM
I never did like the look of the chrome dome seen through the grill of a Twin Reverb! :dont-know:

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

more10
03-01-2012, 10:15 PM
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.

Ruediger
03-02-2012, 12:20 PM
http://www.audioheritage.org/vbulletin/showthread.php?26529-E-140-dust-cap-replacement-advice-please&highlight=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

ivica
03-03-2012, 04:52 AM
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/vbulletin/showthread.php?14501-E120-8&p=148781&viewfull=1#post148781

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

http://alteclansingunofficial.nlenet.net/publications/techletters/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.

Harvey Gerst
03-03-2012, 11:04 AM
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.

tomt
03-06-2012, 02:08 PM
some people put this sort of thing on the cone(s)

to reduce breakup




http://t1.gstatic.com/images?q=tbn:ANd9GcReGkFD-MLUZec6g0g1DmzyRe6Wk6T4Ee28pLuieHpSjO56TNAphxUgAp9 jtA (http://t1.gstatic.com/images?q=tbn:ANd9GcReGkFD-MLUZec6g0g1DmzyRe6Wk6T4Ee28pLuieHpSjO56TNAphxUgAp9 jtA)

more10
03-06-2012, 02:54 PM
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

57BELAIRE
03-07-2012, 05:24 AM
[QUOTE=maxwedge;329742]I never did like the look of the chrome dome seen through the grill of a Twin Reverb! :dont-know:

How's this? ;)

maxwedge
03-07-2012, 07:42 AM
I never did like the look of the chrome dome seen through the grill of a Twin Reverb! :dont-know:





How's this? ;)
Personal preference sir?:dont-know:

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

57BELAIRE
03-07-2012, 08:20 AM
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!

Harvey Gerst
03-07-2012, 10:04 AM
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.

maxwedge
03-07-2012, 10:23 AM
Ok Ok, I love em too!:D
I loaded an Ampeg V4 with 4 E120s for the same reason, way back when.:)

more10
03-08-2012, 12:13 AM
If I paint them blue (aquaplas color right?) I will get banned from the forum? :D

57BELAIRE
03-08-2012, 04:05 AM
Ok Ok, I love em too!:D
I loaded an Ampeg V4 with 4 E120s for the same reason, way back when.:)

cool, but I'm just trying to imagine you hauling that cab from gig to gig....:eek: