How to replace the diaphragm in a 2420?

[Soloford]

I've had my 4343b's for about 20 years and recently re-foamed the 2231h and the 2121h. That was so successful that I've decided to tackle the next step.

I've got a new pair of D16R2421's that I got when I first picked up the 4343b's.

I've read here that after 30 to 40 years, it may be time to refresh the diaphragm...so is there a thread here somewhere that describes how to go about it?

I've got it figured out that I have to remove the upper front blue face in order to remove the 2420's.

Since I'll be placing one of the 4343b's on a shelf sideways, while I'm opening up the speaker cabinet I'll rotate the front 90 degrees, and also move the uhf over to the left side so it mirrors the right speaker. Should be pretty interesting to look at!

[Soloford]

After thinking about this, I probably should have started this thread on the DIY side. Any chance one of the moderators could move it...?

Anyway, the first picture shows the right speaker with the lf and mf drivers removed.

The second picture shows a table full of drivers in various stages of work....

The third picture shows the right speaker with the lf and mf drivers replaced.

And the last speaker shows the left speaker with the lf and mf drivers replaced.

Whoever said that removing the old foam was a dirty job hit the nail on the head. Stuff was like tar. Getting it off the kitchen floor was tough.

But what exhilaration when I fired those babys back up!

[Soloford]

OK, so the first thing I had to do in order to replace the 2420 diaphragms was to remove the front "face"...and in order to do that in this small space I had to build a platform to catch/hold it. And remove the mid-range driver in order to have a handle to pull.... A picture...

[Soloford]

Heres two pictures. The first shows the 2420 and the 2405 side by side along with boxes containing the new diaphragms.

The next picture shows the 2420 after loosening the cap, along with the new diaphragm beside it.

[Soloford]

The replacement is pretty straight-forward. Remove the 4 screws that hold the cap in place.

Gently lift the cap away from the body and lay the horn on its side. (this is the second picture in the prior post)

Loosen the terminal binding screws holding the red and black wires to the diaphragm. (DO NOT REMOVE THESE TWO SCREWS) The wire end is slotted for easy disconnection.

Next, remove the three screws holding the diaphragm in place. Replace the diaphragm with the new one...two locating pins make it easy to put in right. Just remember the marked red terminal gets connected to the red wire.

Re-insert the wires to the binding posts and tighten. Re-attach the cap with its 4 screws and you're good to go.

[toddalin]

You are removing those nice tangentials for the diamonds?

If you have no need for the tangentials, I'll take one. My L/R are tangentials and my center is a diamond.

Don't forget to replace the foams while you are in there. They will probably crumble if you touch them.

[Soloford]

I'm keeping the original diaphragms for now. I may wind up putting them back in. I was surprised at how good condition they were in.

While I was ordering the new parts I also ordered JBL re-cone kits (C8R2235)...so now I have a full set of re-cones and diaphragms...but since I don't think I'll ever part with the speakers I have parts for forever.

Maybe it's just me, but I worry about being able to find parts in the future.

The foam (or whatever) in the horn cap was starting to deteriorate...you can see the gunk on the wires and the screw terminals in the second picture from an earlier post.

I had a bit of trouble getting the second speaker face out...when they were originally built, one of the original face screws got cross-threaded...it was a bear getting out. But I was finally able to remove it and get the face rotated for side mounting. Here's a picture of the repair work on the face after getting it out, one of the offending screw, and lastly a picture of the speaker all put back together...it's up on a temporary stand while I build a shelf for the speaker.

In a very small space, you gotta keep half of the chickens flying all the time!

[Allanvh5150]

I have to ask, why did you opt to put the new foam on the front of the cone instead of the rear?

Allan.

[Doc Mark]

Hi,

I was thinking the same thing, myself. Interesting...

Doc

[Soloford]

I have to ask, why did you opt to put the new foam on the front of the cone instead of the rear?

Allan.

I put it on the front because I didn't know that it should have been put on the back. I discovered this site with all it's information after re-foaming both the 2231h and the 2121h.

I had been to the point of getting rid of the 4343's since they didn't sound very good anymore...due to the deterioration in the foam...and inadvertently discovered that I could re-foam them.

I notice that on the new big JBL's the foam is attached to the front.

I've heard both ways...that it does sound different and that it doesn't.

I've been re-searching this site for a couple of months now, and have developed a plan for upgrading them. I have even gone ahead and gotten a JBL 2235 re-cone kit. (I did notice that they have the foam on the back side.)

What I do know is that they sound amazing again.