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swayzeeee

Attic Find - KLH Model Seven

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Tucked way in the back of my uncle's attic was an old pair of KLH Model Sevens that "dont work". I was told, "You can have them if you want to tinker around with them."¬†ūüėÄ

I got them home this morning and hooked them up: woofers sound fine but the tweeters are barely audible and sound scratchy. First things first, I guess: how do I get into these to take a look at the crossover? There doesn't look to be an obvious way in. The back panel doesn't just screw off...

 

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Very cool speakers - - congrats. I think these have the epoxied immovable "spaceship" woofers. This thread should get you started in learning what you're dealing with, and don't let my inane questions in the thread derail you. I've also heard that a little bit of heat can be useful to dislodge the epoxy behind the rear plate.

http://audiokarma.org/forums/index.php?threads/klh-model-7-sealed-klh-crossover-repair.619340/

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Nice.

The Model Seven is a bigger version of the Model Six, with two tweeters instead of one. Henry Kloss said he "got it right" with the Six, so the Seven, with more bass, should be even "righter." 

But there are problems. Henry Kloss made the Four, Six and Seven with epoxied-in drivers that cannot be removed because the front baffle board is an integral part of the driver(s). And the grille is wrapped around the baffle and cannot be removed. So the only way to get in is from the back. Some people have cut into the back panel, but ra.ra has pointed you to an excellent thread that shows how to get in by CAREFULLY prying off the back plate. 

The old capacitors are most certainly shot and this is probably the cause of the tweeter problems, but if you have any bad tweeters you're probably out of luck. Apparently some of the later Sevens had conventional, screwed-in tweeters. But let's not get ahead of ourselves.

Please be aware that the capacitors shown in the AK thread are DUAL caps. That is, each of those brown tubes contains 2 caps. You can replace each with two capacitors. I would use film caps but the NPEs shown are OK. No need to worry about the resistors or coils--those don't go bad. BUT it looks to me like he used the wrong values. If the old caps read "2 x 2MFD" as it appears, and IF all of the  red leads go to one point and both black leads go to one point as it appears in zephedone's picture, then what you need is just ONE 8uF cap per speaker. I don't have a schematic so don't rush out and buy any caps but when you get inside, carefully trace where those leads go. Kloss was known for buying up surplus caps so if he got a deal on 2x2 doubles when he needed 8s, he'd just parallel them to make what he needed. Maybe one of those old caps is 2 x 1MFD, in which case a single 6uF cap per speaker would be correct (this is more likely, since AKer L200B used 6uF caps). Just check to be sure.

So. Go slow, ask questions, post pictures and have fun!

Kent

 

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I was able to get into the first one of these yesterday following the great, detailed descriptions in the AK link above. It was a bit of a struggle to get the back plate off and there may be a scratch or two on the metal that wasn't there before but... job done. I chipped away the epoxy and found the crossover to be as documented.

The hardest thing for me as a rank newbie was following the wires to make sense of the circuit. First off, the three input wires coming from the terminals were tied into a big double knot, which made following their path kinda frustrating. Then, one wire would go into a wire connector to be split and the two wires coming out would be a different color. For example, the blue wire coming from an input terminal goes into a connector and two black wires come out and connect to the capacitors.  There was a mess of six red wires coming in or out of a big wad of black tape... these had nothing to do with the red wire from the input terminal. Four of them are coming out of the two double capacitors and the other two go off to the two tweeters.

I drew up a picture as I was trying to figure all of this out to keep it straight in my mind, submitted here in case it helps someone else down the road. It's not meant to be as elegant a circuit diagram as the one on AK, it's just so I remember what color wire goes where. 

file6-3.jpeg.084b01cfd417f9e2e0e8042360a52cda.jpeg

file5-5.jpeg.8eb5b9aabbfbd1c2b445c800c8bef184.jpeg

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No worries. We're here to help¬†ūüėÄ

Getting the back plate and epoxy off is the biggest obstacle so you're well on your way!

Those double caps can be confusing. Remove the wad of black tape and also remove the plastic clamps holding the caps. Check the values. 

Be very sure about the values. The schematic posted over on AK shows one TWELVE uF capacitor. If that's so, one of your caps is 2x2 and the other is 2x4. BE SURE TO CHECK. If you have a total of 12uF then you'll need to use one of these for each cabinet: https://www.madisoundspeakerstore.com/carli-capacitors/carli-mylar-12-mfd/

edit: I just asked about this over on AK and THEN noticed 45rpmspinner answered this question in posts #45 and 55. He confirms it is one 2x2 and one 2x4, so 12uF all together. But please do me a favor and check yours, too.

So... assuming all those red wires under the black tape are connected together, and the values add up to 12, just take one 12uF cap and attach one lead (doesn't matter which) to the blue wire that goes to the switch and the other lead to the 2 red wires that go to the 2 tweeters. Solder, crimps or wire nuts will all work. Easy peasy.  You can attach the new cap to the baffle with one of those U clamps if you wish. You want to be sure the metal leads cannot touch any other metal, Then get all the stuffing back in and re-attach the metal plate. You'll have to make sure that plate has no air leaks so seal it with some gasket material (a foam sheet from Michael's makes a good gasket) or duct seal or even caulk. 

Ask any questions.

-Kent

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Thanks! I pulled the caps and they are labeled 2x2MFD and a  2x4MFD, so I would order a 12 uF replacement, right? This seems to confirm the findings in the AK thread, posts #2 and #45. 

file-18.jpeg

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Just now, swayzeeee said:

they are labeled 2x2MFD and a  2x4MFD, so I would order a 12 uF replacement, right?

Right!

Those Carli caps I linked at Madisound are good caps and inexpensive. Or you could use any of these, from Parts Express: https://www.parts-express.com/cat/metalized-polypropylene-crossover-capacitors/294?N=22074+4294967118+4294962382&Ne=10166&Nrpp=99999&Nrs=collection()%2Frecord[endeca%3Amatches(.%2C"P_PortalID"%2C"1")+and+endeca%3Amatches(.%2C"P_Searchable"%2C"1")]&PortalID=1

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This is the foam sheet sold in Michael's and other craft stores. You can cut out a nice gasket: https://www.michaels.com/12x18-foam-sheet-by-creatology/10597484.html?cm_mmc=KidsPLASearch-_-google-_-MICH_National_Kids_Shopping_Null_Null_All+Products_General_MIK-_-Kids&&cm_mmc=KidsPLASearch-_-google-_-MICH_National_Kids_Shopping_Null_Null_All+Products_General_MIK-_-Kids&gclid=Cj0KCQiA14TjBRD_ARIsAOCmO9a9FNdeobL_2h2iO1owCkicU0KjaCe-0PRVGiN5nVhSt78W4SUBa-8aArkfEALw_wcB&gclsrc=aw.ds

You could also use Duct Seal. It's like the plasticene modeling clay kids use https://www.homedepot.com/p/Gardner-Bender-1-lb-Plug-Duct-Seal-Compound-DS-110/100212441  or window putty if you have some on hand.

You could use weatherstripping if you have some thin stuff on hand but the foam sheets are thinner and cheaper. https://www.amazon.com/Frost-King-Vinyl-Foam-Tape/dp/B000BQRQA0

You could use caulk if you have it on hand. The idea is to make sure there are no air leaks. I like the craft foam sheets, especially for a rectangular gasket. Cheap, easy to work with and easy to remove if you need to get back in there.

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Very important points from 45rpmspinner over on AK:

Quote

Btw, my advice above about leaving the factory wire-nuts in place when possible is golden.
In my experience those connections are at least as good as anything you're going to able to do with a soldering iron, one-handed, blind, inside the box.
The more you pull the wiring apart, the more you may regret doing so.

The other thing worth mentioning is that the color coding on the wires isn't consistent.
If you end up scratching your head over the tweeter leads [both of which are red]....the one with the knot in it is the positive lead.

I use hot glue to position the resistors on the back plate after the epoxy has been chipped out.
Don't lose the rubber washers which go around the speaker connectors.
Check to see if there's continuity between any of those connectors and the plate afterwards.
If so, that's bad. Redo if need be.

 

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In that referenced AK thread, that whole mess of wires and different value dual caps had me totally flummoxed. Now that it's all figured out regarding correct replacement cap value, perhaps this is a good place to post the original schematic for future restorers. This diagram makes it all look so simple. :rolleyes:

KLH_Seven_xo1.jpg

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