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Thread: L-150s Restore and Recap

  1. #16
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by couldbfishin View Post
    I really think I need to do something with the speakers, and I am thinking recap. They are 37-40 years old.

    What do you think?
    I think a re-cap or looking at sources and amps are great ideas once you fix your speakers. Think of them as icing on the cake. First you need to make sure the cake is edible.

    The woofers are wrong and the high frequency drivers have been seriously physically abused and likely electrically abused as well.

    I would disassemble them and carefully test each driver and verify which drivers and cone kits you have.


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  2. #17
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    Smile L150 with curious woofers turn out to be 128H with black coating on back of cone

    I removed a Low Frequency Driver from one of my L150 speakers to identify it. I have been curious as to why it doesn't have the white coating on the front of the cone like other L150s do. I was concerned that a previous owner had substituted non-JBL drivers.

    What I found was that the driver is marked JBL, 128H, and has a serial number. It looks like an original JBL, not rebuilt. It looks very clean, almost new, although I have owned the speakers for 15 years or so.

    I feel relieved that they are original JBL 128H drivers, or at least this one is and I am assuming the one the other speaker is like this. But, there is still a mystery about why these are installed and not the white coated 128H's.

    I have read these were used in some of the studio monitors, and that they are identical in performance to the 128H's with the white coating on the front. Maybe it was a substitution at the factory, due to inventory or something, or maybe some previous owner swapped the white coated 128H's out for the black coated 128H's at some point. But, I am just glad that they are original JBL 128H drivers and they are in such good shape.

    I will try to attach a short video of the back and front of this driver. I will also attach some photos in case the video does not work.

    I have been looking for replacement 033 tweeters on eBay and found a couple for $60 each, that are used but look real good. If you know of other sources, at lower prices, please let me know. I don't know what a reasonable price is.

    Thanks to those of you who responded.

    Maybe someone else will have some of these black backed 128H drivers and this thread will help them.

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  3. #18
    Senior Member grumpy's Avatar
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    While indeed a 128H frame and magnet, it appears they were re-coned with aftermarket parts at some point. The black-front version is a 128H-1, the aquaplas is tinted black and applied to the front of the cone, which the provided photos don't appear to show. The large dust cap and glue-line is another indication that the recone did not use JBL parts. Doesn't mean it won't sound OK. Pic of 4412A (128H-1) woofer attached for reference. L150 is a fun speaker. I bought the -A version when it came out.

    Likely the original foam surrounds needed replacement, and the owner had them "inexpensively" repaired (vs the cost of a JBL re-cone)... may not have been offered a resurround as a choice, or the coils could have been damaged. At any rate, sorry to be the bearer of unhappy news.

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  4. #19
    Senior Member Chris Brown's Avatar
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    Looks like you have some weird stuff going on with your passive radiators also. Neither looks like an original PR300 passive radiator. In addition, the two shown in your pictures are different. One seems to show a ribbed cone with the foam glued in back, and the other appears to show a smooth cone with the foam glued in front. The passive radiators are crucial to proper tuning of the speaker. The PR300 comes with weights on the rear that can be adjusted to tune the bass - similar to shortening or lengthening the port tube on a ported system. Using a different passive radiator with a different cone could change the sound also. Likely these passive radiators weren't installed with any consideration as to this effect, so who knows how they are changing the sound of the speaker. Mismatched passive radiators throw another element of randomness into the mix.

    If you end up not being able to locate any 033 tweeters, another possible option you could look into is the 034. It fits without modification and is listed by JBL themselves as a replacement when the 033 is not available. I feel that they sound just as good as the 033. The only catch is that the 034 has a plastic front whereas the 033 has a metal front. There is no sealed tweeter chamber in the L150. That causes the whole 034 tweeter to vibrate almost like a mini passive radiator at loud volumes. If you either re-enforce the plastic frame of the 034 somehow, or improvise a sealed compartment behind the tweeter, it should be possible to eliminate any issues. I would still go with the 033 but it's nice to have a 2nd "better than nothing" option if it comes down to it.

    One of those mids looks like it might have a tear in the cone. You might keep an eye out for some. Keep in mind that many of the even numbered LE5 mid-ranges are interchangeable. LE5-6, LE5-8, LE5-10, and LE5-12 are all acoustically identical, the only difference being some have a a black front, some have a silver front. You might try using a small vacuum hose to pull out the dust cap on those mids, and you could even try that to pull the dome of the 033 back out.

  5. #20
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    L150s sound better now

    I reinstalled the Low Frequency Driver we've been talking about. I then worked the controls for the mid and high frequency drivers. They sounded dry and a little bit scratchy at first, but loosened up some after about 5 minutes of back and forth.

    Then I used some duct tape and carefully pulled out the dents in the mid and high frequency drivers. I tried a shop vac on the 033 high frequency driver, but it wasn't working. So I went back to duct tape and patiently got the dent to come out.

    I then turned on the turntable and Marantz 2275 and magic, the high frequency drivers are working again, and the mid's sound much better also.

    I found a guy on eBay selling some 128H-1 drivers he rebuilt. He says in the description that he refoamed them, but doesn't mention installing new cones. What was interesting is that the cones had the black coating on the backside just like mine. So, I sent an inquiry to him to see if can identify my low frequency drivers. Are there replacement cones with the coating on the backside? Maybe he can shed some more light on what has been done to these drivers.

    Thanks for pointing out the difference in the cones on the passive radiators, I had noticed it. Both seem to be working, so that is the least of my concerns at the moment. I will lean more about matching them later.

    I had not noticed the tear in the LE5-10 mid range driver. Someone evidently repaired it with fingernail polish or something similar. It does seem to be airtight, and working. But, as soon as I find a good one I will replace it.

    I will always wonder what caused this damage to these speakers. I am assuming kids, and not cats, because of the pushed in dustcovers.

    I still plan to replace the caps, so if anyone can recommend a good brand of replacements, please let me know. I will attach a photo of my crossover, as best as I could do sticking my phone up inside of the speaker cabinet.

    Next order of business is pulling drivers on my L110's to see what they are, and if the cross over is original. I want to order parts for both sets of speakers at one time, and then replace them.

    After reading another thread about using integrated Mac gear from the 70's with a pair of L100's and how good it sounds, I plan to hook up my recently restored Mac C20 preamp and MC-40 mono block amps to the L110s and see how they sound. The amps put out a minimum of 40 watts, but they are very clean. Hopefully the matchup will sound good.

    And, I have decided to move the Marantz 2325 receiver back to the living room so I have some more wattage driving these L150s and see if that improves the sound. It is 125 wpc versus the 75 watts per channel driving them now. Marantz gear is pretty clean also and typically understated in power.

    Thanks and if I learn more about the black coating on the backside of the drivers, I will keep you posted.

  6. #21
    Senior Member grumpy's Avatar
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    I think what you are seeing on the cone backside is just the raw paper pulp, not a coating.

    Also, in past posts I may have made statements or repeated info indicating aquaplas on the cone backside for 128H-1... given the 4412A photo I just took and others I just went back and reviewed, it appears that was incorrect and black/dark-gray aquaplas on the front was how they came from the factory.

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