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Thread: C38 Detailed Blueprints?

  1. #1
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    C38 Detailed Blueprints?

    I was hoping to find the "detailed blueprints" that are talked about in the docs here http://www.lansingheritage.org/html/...ns/c35-c39.htm

    Does anyone know if those plans were ever scanned and saved? I have a pair of C38's I am about to repair.

    Thanks!

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    Quote Originally Posted by iliveinyourhead View Post
    I was hoping to find the "detailed blueprints" that are talked about in the docs here http://www.lansingheritage.org/html/...ns/c35-c39.htm

    Does anyone know if those plans were ever scanned and saved? I have a pair of C38's I am about to repair.

    Thanks!
    The plans you posted in your comment are the same plans I used to build a pair for myself. The early C model bass reflex enclosures are not complicated to build. As for detailed blue prints, they probably went into the dumpster with every other piece of vintage documentation prior to the Northridge earthquake. The company used the timely earthquake as a cover story to explain the so called, "flooding" of the document department.

    What would be the nature of the repairs?

    H.F.

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    Thank you for the history lesson that really does help. (not vein sarcastic)

    Both cab's have been sent to the woodworker today, hopefully he can salvage them. Both of them are dried out pretty bad and missing the bottom of the front frame.

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    Quote Originally Posted by iliveinyourhead View Post
    Thank you for the history lesson that really does help. (not vein sarcastic)

    Both cab's have been sent to the woodworker today, hopefully he can salvage them. Both of them are dried out pretty bad and missing the bottom of the front frame.

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    Simple fix. JBL used what is called a locking miter joint. It's an expensive cutter which requires a bit of setup. Nothing can be done about the dryness, the particle board JBL used does not hold up over time even under the best of conditions. Using biodegradable adhesives didn't help either. On the Hartsfield and Paragon drawings the company referred to it as, 'Timblend'. Fancy name for something equivalent to a hotdog.

    If I were repairing your speakers, I would take a heat gun and remove the veneer on the total front edge face and replace it with a new flitch of veneer, not paper back, unless your woodworker is adept at grain matching a patch job. Personally, I like to keep repairs as original as possible. The problem with replacing veneer, is that the original veneer is old growth, and finding a new piece of veneer that will be a grain and color match is time consuming. On my cabinets I used solid hardwood as front edge banding around the perimeter because of the weakness of the bottom piece.

    H.F.

    BTW - Is that the original grille fabric?

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    I assume it is original fabric.

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    Or heck here is the whole set http://public.fotki.com/rooted/jbl-c38-d130075/

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    Anything else cool you can clue me in on this pair based on the pics? One cabinets SN plate was all flaked off but the SN's of all the components are super close (less than 10, if not sequential).

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    Quote Originally Posted by iliveinyourhead View Post
    I assume it is original fabric.

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    Or heck here is the whole set http://public.fotki.com/rooted/jbl-c38-d130075/
    Man, those look pretty rough, but I've seen worse. The earliest the enclosure with the Energizer cutout could have been manufactured would have been 1963. The diecast labels also are a tip off to how old they are, including the legs, neither of which were used in the 50's. The boxes are definitely 60's vintage. I have seen die cast labels on Ebay now and then, including counterfeit C38 inserts without serial numbers, should you wish to have the boxes completely restored. I noticed one of the glue joints has been compromised, that definitely needs to be re-glued. It probably isn't the only one.

    Now for the legs. If you have a hand drill, secure the stud in the chuck not so tight as the crush the threads. You can either use course steel wool, or course Scotch-brite to put the luster back as it originally was. I suggest wearing gloves, as either abrasive you chose will get a little toasty. It appears by the corrosion, that the legs might have been in a damp or salty environment for quite a spell? Patience will be required to remove the corrosion, and there may possibly be pits in the aluminum. You will be hard pressed removing those if they are present.

    As I suspected, and why I asked, I do not believe the fabric is original. Also, I don't believe the grille frames are original either, but I am unsure when or if JBL switched from the window screen frame to a wooden frame before the C series bass reflex systems were discontinued at the end of 1969 or so. They were not in the 1971 consumer catalog line up. The fabric appears to be the same style that was used on Klipsch enclosures, and similar to the same fabric that was used on Soldano speakers and amplifiers up until about a year ago. Another clue, the haphazard fashion in which the staples were applied. Not very pro. It usualy is a result of someone trying to hold tension on the fabric, while wielding a manual Swingline stapler. By the style of the staples I'm probably right.

    As for the re-cone you obviously need. There is no JBL kit available for the D130, the best you can do is have the E130 kit installed if there is no issue with the voice coil gap. The closest other kit I would recommend would be the 2220 kit with an aluminum dome, and again, depending if there is a voice coil gap issue. The 2220 save for the linen surround, is a dead match in all respects to the 130A. There is an outfit in Arizona that sells drop in kits for the D130F, but the D130F does not share the same Thiele-Small parameters as the D130. Also, I have yet to see any outfit that offers after market JBL re-cone kits provide T-S parameters to support the claim their kits are the same as JBL. Until they publish T-S parameters on their kits I hold them suspect.

    Regards, H.F.

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