JBL 120 Dustcap replaced

JBL 120 Dustcap replaced

Postby tatittle » Sat Jul 09, 2016 12:55 pm

hey Now, I am guessing there is at least 1 or 2 other folks here at GDMS who have 12" and 15" JBL's that have dented aluminum caps. I am about to attempt to replace one with a slightly larger diameter so that it sits evenly without too much trouble. Thanks to wALDO for the connect:

http://www.soundspeakerrepair.com/mm5/m ... e=Aluminum

I figure I would try and document my battle with a few photos and upload them here for others to inspect. So give me a few days, in the meantime has anyone else had success doing these?
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Re: JBL 120 Dustcap replaced

Postby playingdead » Sat Jul 09, 2016 1:50 pm

I have not replaced one personally, but saw it done on my E-120s a couple times at a local JBL authorized service place. It took, literally, about 10 seconds. They cut the old one right off with an X-Acto knife, flowed in some black glue from a little squeeze bottle and stuck the new one down. Done. They charged me $5 if I remember correctly. I was like ... "That's it?"

Kind of made sense. The dustcap has very little to do with the mechanics of the speaker it's just keeping dust off the coil. As long as it's not rubbing or scraping it shouldn't really matter if it's dented.

The one referenced below fits over the old one? So you just leave the dented one on there?
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Re: JBL 120 Dustcap replaced

Postby tatittle » Sat Jul 09, 2016 3:40 pm

Its unbelievable how much more sensitive JBL's are than typical vintage Jensen style drivers. I just put 2 x 12" D series in a cab that had 2 x Rola's or something (sound pretty nice) and it like the amp has twice the wattage or something!

Hey whats the name of that picture cloud people use here? My files are too big...also.
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Re: JBL 120 Dustcap replaced

Postby tatittle » Sat Jul 09, 2016 3:49 pm

http://i1358.photobucket.com/albums/q77 ... inzhh4.jpg

http://i1358.photobucket.com/albums/q77 ... yriro8.jpg

Pictures BEFORE

No, I am going to remove almost all of the old one with the sharpest razor I can find. I was amazed that this speaker's dustcap seemed to spontaneously tear with use after it was initially dented. Maybe pulling those caps out with tape or whatever is the way to go if your not gonna replace the it.

Ive also been rolling. On tubes that is, but its just as fun! I've audtioned some classic ones and even a rare European one that seems to suit Garcia tone especially well. I thinks some folks stray away from discussing tubes in forums cuz of the limited supply of vintage tubes, but if you wanna talk tubes PM me :) I've also done a round of fresh fretwork and I cant tell you how happy I am with them. A decent set of files is a must for the do it yourself guitarist. Though I might try and go with steel frets on anything new. Ive been busy finally...I also did the tremelo/vibrato off mod to a BF Fender which gives it a gain boost merely by taking the tremelo/vibrato out of the circuit with a switch. Very clean work lol. Anyone try a resonance control mod for Master Volume Fenders? ThaT'S NEXT i GUESS.
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Re: JBL 120 Dustcap replaced

Postby tatittle » Sun Jul 10, 2016 1:27 pm

Here isn the replacement cap. There is also a couple 8" replacement caps for D208/216 in the small box in photo.

http://i1358.photobucket.com/albums/q77 ... mk0rwi.jpg

http://i1358.photobucket.com/albums/q77 ... x1ybxq.jpg
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Re: JBL 120 Dustcap replaced

Postby tatittle » Sun Jul 10, 2016 4:56 pm

OK Here are some more pics. Photos of speaker after dustcap removed via razor; and photos of mounted dustcap with weight to keep it snug for glue drying. Oh yeah, and my reward for bravely tackling this project :)

http://i1358.photobucket.com/albums/q77 ... jvsfgc.jpg

http://i1358.photobucket.com/albums/q77 ... jvsfgc.jpg

http://i1358.photobucket.com/albums/q77 ... j6qf5k.jpg

http://i1358.photobucket.com/albums/q77 ... rguujr.jpg

The actual cutting of dustcap was pretty tricky. It is fairly thick aluminum to slice through so one is liable to use pressure to get the cut started and then in slides somewhat uncontrolled until pressure is released. I tended to cut more down on it than thru horizontally and that may not be the best technique. The voicecoil is VERY close to the break angle of the dustcap where one is trimming. There was a few scraps of aluminum I had to clear out of the magnet after removing cap. The magnet becomes very strong, especially after aluminum cap is remover so beware: it is strong enough to pull your tool away from your target, especially at first before you expect it.

Applying the glue wasnt that delicate. There is a natural valley between the old dustcap edge and paper cone it settles into naturally. I used the instructions available through Simply Speakers etc. The new dustcap didnt sit perfectly flat against the cone, I need significant weight to close the gaps some places. I could have applied a bit more glue to better seat the cap. I may go back and apply more glue from outside if I doubt to seal as is. I also was left with some faitly ragged edges on the old cap; I hope they dont cause any trouble. I just left them alone figuring I would only make things worse trying to clean them up. I will leave glue to dry overnight. The glue actually began to dry quickly: I stopped to clear some things for 45 seconds and the glue I laid before I paused dried a bit different color/rate. Hopefully it was still plenty sticky to hold new cap.
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Re: JBL 120 Dustcap replaced

Postby tatittle » Mon Jul 11, 2016 1:36 pm

And finally the dustcap I cut-out, and the completed speaker after putting another bead of glue around outside edge of dustcap after installation. This is even harder to get looking perfect like the original D120's, mine looks more like an E120 as I think they started gluing from outside with those. Good luck! Should sound fine but havent tried it yet.

http://i1358.photobucket.com/albums/q77 ... ya8ubs.jpg

http://i1358.photobucket.com/albums/q77 ... 9y3hyn.jpg

Finally, the replacement caps I bought from SoundSpeaker or whatever don't have the quality control built into the original JBL process. I found a tiny dent in mine and another raised imperfection about the same size. It is very small hard to see even, but I always prefer to avoid all imperfections.
Easy to moderate (for inexperienced) difficulty.
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