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Model 6 Restoration


Brad1234
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I am working on another KLH Model 6 restoration (stamped 1967 for the year on drivers) that I got on ebay for relatively cheap. This time I'm working on the model with the removable woofers. These speakers showed up in remarkably good condition, even the original grills are still in good shape!  
 

I am refinishing the cabinets and replaced the 8uF tweeter caps, the other 2 (2uF) caps are buried in epoxy with the switch on the back of the cabinet, so not planning to change them. Anyone have experience with changing those caps buried in the epoxy?  
 

The coolest thing I found about these speakers is one of the previous owners taped the original owners manual on the back and I was able to remove it and fold it open to reveal the original manual still in good condition, pretty cool!  I got the woofers doped and sealed well, finished one speaker and working on second tomorrow. I have attached photos for your entertainment. 

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Correction on this post, looks like there are no caps in the epoxied speaker terminal cover, I measured it and there is no capacitance, just resistors, 3, 6 and 14 ohm. I had the wrong KLH Model 6 wiring schematic. 

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Not sure I understand your post, Brad. I've never seen a KLH 6 without caps in the tweeter circuit. There is no quicker way to burn out a tweeter than to omit the capacitor(s) from its circuit.

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Hi Roy, there is an 8uF cap for the tweeter, but the wiring schematic I have for my other sixes has 2 2uF caps in addition to modify signal to tweeter with switch. I tested the leads and no capacitance was measured at any switch position, making me think there r just resistors on the switch?  I attached the photo of the diagram I got online for the 6. 

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Check this post. I missed the 2uF caps too but you have to break the epoxy (?) potting 

 

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4 hours ago, Brad1234 said:

Hi Roy, there is an 8uF cap for the tweeter, but the wiring schematic I have for my other sixes has 2 2uF caps in addition to modify signal to tweeter with switch. I tested the leads and no capacitance was measured at any switch position, making me think there r just resistors on the switch?  I attached the photo of the diagram I got online for the 6.

Most meters will not measure capacitance when they are inline with resistors. Whatever the case may be, I would wire them in accordance with the schematic showing the 2uf caps.

Roy

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Thanks Roy and Kent, I should have done my homework on this forum's past posts!  Ah shucks, I already sealed the speakers back up. Looks like I will have to open them back up again and break up that epoxy.  I forgot the caps wouldn't register with the resistors connected. I am a little disappointed with the "half-way restored" sound from them so I need to get those 2 epoxied-in caps replaced.  Thanks so much for the help!  

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I got the epoxied switch plate out with a screwdriver and hammer, it popped off pretty easy working from inside of the speaker. Found the tiny cap to replace. Attached some pics. Im going to replace resistors too, i know I dont have to, but they are so cheap.
 

I was thinking of just using the black seal-n-caulk rope stuff around the edge of back speaker hole before screwing down the plate to get it air tight. It works for the drivers so should work on back plate with using screws in place of nails. What do yall think?

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Got the 2 new caps in for the switch plate and all sealed back up. Wow, what a difference in sound quality with replacing those 2 caps hidden in the epoxy!  These speakers sound incredible, the vocals and mids are so clear, truly blown away and so happy I restored them. They sound better than the earlier epoxied woofers Model 6's I also have. 
The grills appear like they may be original and have held up very well. They had light staining around the woofer cutout u can see in the earlier pic. I took a gamble and tried wiping that area with a cloth wet with bleach water and let it air dry. Much to my surprise the staining has disappeared from the light coat of bleach water!  See new pics of grills. 

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Excellent! I really liked the Six but couldn’t keep them. Too many speakers and not enough room. Yours look great. I’ve always been afraid to try bleach on grilles but you give me confidence 🙂 Any estimate of the water to bleach ratio?

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JKent, I used a quick pour, probably about 2 shot glasses worth (about 60ml I estimate) in half a sink basin filled with cool water. Then used a rag to wipe it into the area of the grill that had the staining and scrubbed a little, then wiped around the area some to blend it a little. It looked horrible when wet after wiping, but dried to match rest of grill to my surprise.  I dried it indoors, not out in the heat, to give bleach time to work. Good luck if you try it out!

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  • 2 weeks later...

Thanks Jake. It's not that bad if you have a solid plan for the steps. I assume u have the removable woofers?  First u remove the woofer and stuffing, document wiring (w photos), undo twisty ties for tweeter, 8uf cap and inductor, get a screwdriver and hammer and chisel out the back terminal plate (careful not to dent it) until it pops out on back, then pry it out and chisel off all the epoxy around resistors and caps. Once u have the plate off its easy to solder on new caps and resistors. A lot of people dont replace the resistors since they dont usually go bad, but they are very cheap so I usually do. 
 

I used the black "caulk n seal" rope caulk (from parts express) for woofer sealing on the back plate with screws instead of nails to secure it airtight, and used the rope caulk on the woofer and tweeter. Then dope ur woofer surrounds with vintage AR surround sealant if needed. Then ur speakers are as good as new!  If ur gonna refinish the cabinets then its best to do that while the drivers are out too to keep dust away from drivers. This is probably too much info but I like to help other vintage speaker enthusiasts as much as I can, and this stuff is a fun hobby of mine!

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On 8/4/2022 at 4:46 PM, Jakeabean said:

I'd like to replace the caps in those, but not looking forward to the operation.  Looks like a lot of trouble. 

Yeah, that's where I was about 2 decades ago when Wanted to restore my first speakers, AR-4x's. Folks here were VERY helpful. It's not hard as long as you have guidance.

Kent

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Well, guess I'll have to break out my Binford 2000 electric hammer and chisel assembly, and get to work on mine. Anybody got a list of what I should order as replacements before I begin this operation? Or... are there sometimes different caps depending on build date?

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AFAIK, all Model Six's have the same crossover components. Certainly, my early (epoxy woofer) versions have the same parts as Brad listed (8-2-2uf caps + resistors & switch) earlier this thread and I've never read of any Six owner discovering different crossover component values in their unmodified speakers. It seems like the part that typically fails is the 8uf capacitor, the others, rarely.

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7 hours ago, jessiAV said:

AFAIK, all Model Six's have the same crossover components. Certainly, my early (epoxy woofer) versions have the same parts as Brad listed (8-2-2uf caps + resistors & switch) earlier this thread and I've never read of any Six owner discovering different crossover component values in their unmodified speakers. It seems like the part that typically fails is the 8uf capacitor, the others, rarely.

My experience is that the KLH Six was always built to the published schematic. I have two pair of Six, one 17, one 20, one 5, and one 12. I have not found any deviation from the published schematics in parts values for the caps and resistors. I don't have any way to measure inductance, but that should never be an issue unless there is visible damage to the inductor.

I disagree about the 2 uF caps not failing. They fail at about the same rate as the 8 uF cap. The 8 uF cap is in series wth the driver, so a failing cap will likely be very audible, particularly if the ESR increases, as those caps are known to do. Replacing the 8uf cap will often result in immediate sound improvement, but it is likely the 2 uF caps are still adversely impacting SQ, but to much lesser degree.

The 2 uF caps are in series with resistors and that part of the crossover performs a shaping function. Because the caps are in parallel, a change in ESR will be limited by the resistor value, thereby limiting the attenuation from failing caps. If the 2 uF caps fail entirely or just drift, the only impact will be on the crossover frequency of the shaping circuit. Such changes are rarely audible and generally require test equipment to detect the change in FR.

Bottom line, replace all caps and don't worry about it.

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11 hours ago, RTally said:

I have two pair of Six, one 17, one 20, one 5, and one 12.

This is a little OT but I'd be interested to know how you rate them. I've had all of those models but no more. I really liked the Twelves but didn't have room for them. I liked the Fives very much and sometimes regret selling them. The Seventeens and Twenties are essentially the same speakers but the 20 is 4 Ohms. Nice but I prefer my AR-4x's in that class. The outlier is the Six, which I never really listened to much--just restored them and sold them. I didn't have room for more speakers but owners of the Model Six really seem to like them.

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Oops. Typo. I have Model 23, not 12. I've been looking for Model 12, but no luck yet.

I have not finished restoring the Model 5, 17, and my epoxied woofer Model 6 yet. 

I am really impressed with the Model 20. I power them with a Denon amp that has 200 wpc at 4 ohms. They compare very favorably with my newer Model 6, although the Model 6 goes deeper. This is not surprising because the 6 and 20 have the same type of tweeter, with the 6 having a larger cabinet.

My Model 23 has been recapped, but the woofer has not yet been re-coated. Even still, it sounds fantastic. The Model 5 is still original with no restoration. It sounds good and I can only imagine how they will sound after being restored.

All my KLH are keepers. I will have to do a proper comparison after I get them all restored.

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Nice, interesting combo of KLH and Advent. Wonder how it sounds?  Also, that tweeter could be repaired with a a little solder on the wire. I have saved a number of tweeters by carefully soldering that hair-thin wire back together. Did u also recap the 2 caps on the tweeter switch by the terminal connections?

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The advent case  looks nearly identical to the model 6. Not surprising as it was designed by the same person and built in the same town. Probably a clone. 
 I haven’t done the 2 4uf caps yet just the 8’s on the tweeters. It sounds great though so I might not. 
one  of the tweeters is good so I’m going to try to solder the bad one. No loss if I bungle it. 
this has been my I quit cigarettes project.  Keeping my hands busy. 

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