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Thread: Old Shearer Horn, Altec, VOTT Found, And Question

  1. #31
    Member Flamingo's Avatar
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    04-19-2020 Update

    ​I've had some quarantine time to work on this project. Finished cleaning the H1505 up, figured out how to build and mount it onto the top plate so it doesn't actually modify the 30W5 while still fitting securely, and putting together semi-old hardware for adjustment capability. The bolts are mounted through the plywood veneer for strength, this horn-plus-driver-plus-plywood weighs north of 150 lbs.

    Attachment parts are not original Altec-Lansing, but neither is the top plate. My goal here is to be able to assemble a working system so I can hear its basic sonic signature, leaving the original parts intact for a future collector.

    I built the gaskets out of new cork rubber, found some old 5/16"-24 bolts for the throat, and some old '60s vintage fiber-rubber gasket material that matched the horn flange thickness exactly.

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  2. #32
    Member Flamingo's Avatar
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    I use SMAART 8 for and a couple different reference mics (mainly earthworks) for general measurements, so that's what I set up to work with the 816A/MR64 combo as well. I only have the one 1980s vintage 288-8G driver that came with the MR64, so I'm sharing this driver between the MR64 and the H1505 for now. Bolt it on, do some measurements, move it to the other one when needed.

    The original Altec-Lansing diaphragm was pretty dinged up from when someone broke a terminal off - magnet sucked the nut right into it. Needed a replacement. As mentioned earlier and in an effort to save money, I bought a Simply Speakers replacement diaphragm, thinking it would be good enough. Feel free to say "I told you so", but I've had problems with it.

    It actually rubbed in the gap the first couple of times I installed it, even after re-centering it (using the low-level 250 Hz sine wave approach). I think the VC just goes out of round when it overheats, which doesn't take much current to accomplish. As long as I don't get too loud, the HF just seems a bit "raspy." I think the SS "stamped surround" vs. the original hydroformed spiral makes a difference in the sound quality, so I've ordered a replacement GPA diaphragm, and I expect the HF will be as smooth as the LF on both systems. Is this a reasonable expectation?

    For processing, I'm using a QSC PLD 4.5 four-channel amplifier with good DSP on each channel. Up to 48-dB/octave crossover filters, 5-band PEQ, delay, and limiters are all employed on the speakers. The 4.5 is a pretty beefy amp, so I attenuate the output levels down 16 or 18 dB to get us in the ballpark.

  3. #33
    Member Flamingo's Avatar
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  4. #34
    Member Flamingo's Avatar
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    Once we got the H1505 and top plate assembly rigged, we rolled the 30W5 under it and eased it down into place. For once in my life, something I built fit very well on the first try!

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  5. #35
    Member Flamingo's Avatar
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    More to come later today, including working to get the phase alignment right.

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  6. #36
    Administrator Mr. Widget's Avatar
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    Damn, that is a beast! Keep it coming!
    I'll make more popcorn.


    Widget

  7. #37
    Administrator Robh3606's Avatar
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    Really keep it coming we love this vintage stuff being measured with modern test equipment. Shows you just how good the engineering was back then! Those guys really knew what they were doing!

    Rob
    "I could be arguing in my spare time"

  8. #38
    Senior Member srm51555's Avatar
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    This is such a cool find, thanks again for sharing. Those guys really did know what they were doing.

  9. #39
    Member Flamingo's Avatar
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    288 Driver/Diaphragm Problem

    I ordered and received an 8-ohm diaphragm from GPA and installed it on the 288 over the past weekend. The issue I was having was a breaking up - VC rubbing sound using the replacement Simply Speakers diaphragm.

    Unfortunately, I'm still having that problem with the new GPA, and in fact I'm also getting the edges of the little plastic spacer imprinted into the new diaphragm, grrr.

    I've cleaned the gap.

    I've assembled it and used a swept sine to listen for rubbing / vibrations, but not really getting any. In fact this process with the GPA was the first time I didn't have to move the dia around and tighten it down to get rid of VC rubbing, as I did in the SS dia. I assumed the SS dia must have gotten formed out of round, or God Forbid, the center pole of the 288 was off.

    Bolted it back onto the H1505, fired it up, and it sounded good for a minute or so. But as it warmed up, the scratchyness returned. I then pulled the dust cover off while connected, and that's when I noticed the imprint of the plastic asterisk on the dia. Not deep, but noticeable. I loosened diaphragm screws, and moved it around while listening to music (just the HF output) and found a spot where it seemed to be smoother.

    Put everything back together again, and listened some more, but it still ended up sounding like it was occasionally rubbing or distorting. I'm kind of at a loss, now.

    I've been involved with audio for 30 years, and replaced a few diaphragms, but never had this much trouble. I also confess to not knowing what the purpose of the "plastic asterisk" in between dia and phase plug. See, I don't even know the right word for it besides "plastic asterisk"! Can I get away with not using it to see if that hitting the diaphragm is the problem?

    Here are some pictures, I didn't get one of the imprinting. My question is, how important is that asterisk spacer? Is there anything I need to make sure of during assembly? I'm _pretty sure_ I'm keeping the leads from the terminals to the spades on the dia to the sides of the diaphragm when installed, but can't be 100% sure. Is this even possible for what the symptoms are?

    Any and all help would be appreciated!
    Brad
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  10. #40
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    You might call GPA, but I think that's just packaging protection, I can't imagine it being mounted between the diaphragm and phase plug.

    I only found one other pic, no mention of installing that in the driver

    https://images.reverb.com/image/uplo...gel50xjk9g.jpg

  11. #41
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    That plastic shim doesn't permanently live inside the diaphragm/magnet assembly.

    That plastic "asterix" is simply a VC spacer that's used to help achieve the best alignment of the coil within the gap.

    It's insertion is only temporary ( like when a woofer is reconed ).

    From what I can see, you can't even use it on your older alnico magnet type 288 .

    Here's a snipet of the directions for it's usage ( it has the important points ) .



    The shim is meant to be used with the newer drivers ( ceramic magnet types ) that have diaphragm locating pins that are themselves adjustable.



  12. #42
    Member Flamingo's Avatar
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    Well, this is the part where I go to the corner stool and sit with my pointy hat on

    The spider shim was installed between the old dia and phase plug when I took the driver apart. My initial search of what it was for turned up nothing, so I put it back in like I found it. Which also means it must have sounded like crap when it was actually in service back in the late 1970s/early 1980s.

    That extra 1/32" of material in there totally explains why I always felt like the HF was hit and miss (randomly blocking phase slits), and the VC actually rubbing probably all the time.

    Thanks very much, Earl K, I will let you all know how a slightly marred GPA diaphragm sounds in a 288 after I put it back together correctly this evening.

    Sheesh! I will probably frame it, and title it, "Spider Shim Of Shame."
    Brad

  13. #43
    Member Flamingo's Avatar
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    I feel like the guy who bought a used Servodrive sub and posted on the LAB about his problem with only getting one tone out of the sub no matter what he did.

    Turns out the speaker connection used a 120v twistlock connector, so he made an adaptor and plugged it into the wall. It just sat there, reproducing 60 Hz all day long until someone (I think Fowler) finally sorted out what was happening.

    Lol.

  14. #44
    Member Flamingo's Avatar
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    Spider Shim Of Shame

    After installing the diaphragm back into the driver without the shim, the HF sounds amazingly....normal. Thanks for the installation page, Earl K.



    I'll set up the SMAART rig again and take some measurements and play with the crossover again. I had set it up pretty high (800-ish) because it was buzzing below that, and I thought it was some physical limitation of this driver. Actually, it was - it had a spider stuck in its throat.

    Because I haven't replaced an HF diaphragm in years (my EAW and DAS Audio boxes have great limiters in the built-in amps), how severely do you think I damaged the GPA diaphragm where it left a little edge on it from one of the spider legs?

    Once something like that happens, is it essentially stable, or does it cause progressive degradation over time?

  15. #45
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    The spider shim was installed between the old dia and phase plug when I took the driver apart. My initial search of what it was for turned up nothing, so I put it back in like I found it. Which also means it must have sounded like crap when it was actually in service back in the late 1970s/early 1980s.
    No wonder you thought the spider shim was meant to go inside the driver ( since you found a shim there when you removed the original diaphragm ).

    Yep, face-plant time ( too funny ).

    Hopefully you haven't done much damage to the new diaphragm ( measurements will tell the story ).

    Depending on the model ?? you bought from GPA, the most HiFi version is made from softer aluminum that does in fact "work-harden" over time ( especially when used industrially within large horns ).

    - That's why Altec eventually developed the pre-hardened model ( for extended working life ).


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