Another KLH 6 restoration: need help

[zonkerbd]

Hi all,

This is my first AK post, so please excuse any missteps. Sorry, this is a long post. For those wanting to skip the background, please jump to my QUESTION below. I also added a TIP at the end of this post for dealing with the peanut brittle plug.

BACKGROUND
Let me first sincerely thank all of you who have contributed their knowledge, expertise, and tips to this forum over the years! Discovering vintage speaker restoration through this forum has really helped preserve my sanity during my days holed up from the pandemic this past year. Although I must say at this point it’s now become a borderline obsession, with a pair of AR 4x’s and KLH 17’s under my belt, both brought back to life (recaps, resealing and cabinet work) to sound and look beautiful!

It was during my research on my KLH 17’s that I discovered the curious design of the early model KLH 6’s with their drivers epoxied to the baffle, peanut brittle square plug, and non-removable grilles. (As others have stated, “what was Henry thinking?”). I made a mental note early on “make sure not to pick up any of these by mistake”. Well silly me, after recently coming across a pair of 6’s on CL that “didn’t work” but cabinets in what looked like mint condition for cheap, and after reading that Henry thought he “got it right” with the 6’s, I decided, what the hell, I guess I’m ready for a new challenge!

So I now own a beautiful looking pair of early model KLH 6’s, that do work but both with diminished sound from the tweeters. The serial numbers are far apart (20xxx and 30xxx), but cabinets look identical and both have rusted coloring on the grille cloth from age so looks like they have been stored together for a long time. So maybe one was returned and replaced early on after purchase. The 20xxx speaker has the military grade oil filled “tin can” caps, and the 30xxx speaker has the more common “brick red” caps similar to what was in my KLH 17’s. Both have epoxied woofers and tweeters.

The newer speaker has barely any tweeter output (not surprising with this type of cap) The older speaker with the oil filled caps definitely has more tweeter output but still significantly diminished, which surprised me after what I have read about the oil filled caps aging well. So my plan is to fully recap the newer one, and with the older one start with replacing just the one oil filled smaller cap bundled with the switch and resistors. Then compare with the other speaker before deciding to replace the larger 2nd oil filled cap. I also plan to replace all resistors; I know — many suggest just leaving the old ones, but they are cheap enough so thought I would go for it for the first time.

QUESTION - REQUEST FOR HELP
Now my request for help. I stupidly forgot to take a photo when breaking up the peanut brittle and disassembling the crossover of the first newer speaker, so failed to take note of the cap, resistors sand 3-way switch connections. With the 2nd older speaker I did take photos of the crossover and planned to use this as a reference for both. But when comparing my photo with the crossover spec that is included in the KLH 6 manual it does not seem to match (although I must admit I’ve intently studied this KLH 6 x-over diagram and I’m very confused by it.) I read in multiple posts that the KLH 17 crossover is identical to the KLH 6. But in looking at my photos of my earlier KLH 17 work, the connections are different than my KLH 6. And furthermore, the KLH 17 only has the two terminal posts, and not the three like on the KLH 6, so not sure how comparable.

I would greatly appreciate if anyone can provide an easy to understand diagram of the connections of the caps, resistors and terminals on the 3-way switch for the early model KLH 6? In particular, the discrepancy I see is with how the resistors connect to the 3-way switch terminals (i.e, Normal, Decrease, Increase). Thank you.

I have uploaded some photos of the older KLH 6 with the oil filled caps.

TIP
Here is a tip on dealing with the peanut brittle if you plan to also replace the resistors. I first chipped out the block of peanut brittle as others have suggested. I ended up preferring a hammer and old flathead screw driver. I started with a chisel but it cut through one of the wires (not good if you’re wanting to keep track of connections, and the sharp blade of the chisel is not really necessary. (I read how some have tackled the brittle removal using heat to melt it away, but that sounded like you would be left with a sticky mess so I decided against it). Here’s the new bit that I have not seen mentioned before (maybe for good reason!?). After chipping out the bock, I soaked the block of brittle and electronics in rubbing alcohol, which dissolved all the brittle after an hour or two to leave a nice clean switch. Since I wasn’t keeping the resistors or capacitor I wasn’t concerned about how this might affect them, and seems like the alcohol dries pretty clean, so as not to damage the switch. Other solvents would probably also work, but I had alcohol on hand and it’s not very harsh so thought it would be a good choice. After the switch dried completely I sprayed a bit of electronics silicon lube/de-ox into the toggle switch and worked it in there. I expect it will work fine.

 

[RxDx]

Welcome!

The brittle can be more cleanly removed if you put the speaker upside down on
saw bucks- the chips fall out of the box vs. in... The oil caps might be worth re-using.
I haven't always seen that be the case, though.

Make sure to reuse the speaker terminal insulators so you don't short the wires to
the crossover plate.

Here's the xo diagram that should help you understand the 3 terminals.

 

[Tim D]

With the jumper in place the cross-over on the KLH Six is 90% the same as the KLH 17. The difference being that the 17 doesn't have the inductor in the woofer circuit.

That jumper is for an early capability to bi-amp the speakers.

 

[zonkerbd]

Thank you for your reply, RxDx! Good point regarding working on the speaker with plug facing down to let the bits fall outside the speaker. Fortunately I have a powerful vacuum with a long skinny end that works pretty well to clean up any bits making their way inside the speaker, after removing the insulation.

Regarding the connections, the diagram you posted is the one that I’ve reviewed and am really confused by. Here’s the information I need to know, expressed in a table. I.e., which 3-way switch terminal does each end of each resistor connect to? This isn’t clear to me from that diagram.

End1 End2
3ohm Resistor 1: B post {Nor|Dec|Inc}
3ohm Resistor 2: {Nor|Dec|Inc} {Nor|Dec|Inc}
7.5ohm Resistor: {Nor|Dec|Inc} {Nor|Dec|Inc}

Thanks.

 

[zonkerbd]

Sorry, that table didn't format like I intended, but hopefully you get the idea.

 

[RxDx]

You'll probably have to do continuity tests on the switch to see which
terminals on it are connected in the three different positions. Then it
should be fairly easy to copy the diagram and get the connections
right. I don't have a switch in front of me, or I'd probably be able to
help more.

 

[zonkerbd]

Sorry, I guess I need to learn how to read those crossover diagrams. To me, all the resistors have some line of connection to all three of the switch positions.

I do have a multimeter, but sorry don't know how to test continuity of the switch positions and map that to Normal, Decrease, Increase. However, if they were consistent when making these switches such that the "CARLING" label is always on the left side when the switch toggle is facing out and in the upright position, that gives me the position for how the switch is oriented. But would appreciate any tips for how (1) how to decipher the lines from the resistors to the switch positions in the diagram and (2) how to test continuity/mapping of the switch with my multimeter. Thanks.

 

[RxDx]

Looks like the blue wire goes to the center terminal on the switch. Connect one lead of the meter
to it. Connect the other lead to the "top" terminal (in this picture), and see which switch setting
gives you continuity between the center and top leads. Figure out what that switch position
represents. I'm guessing that requires knowing how the switch sits in the terminal plate. Let's
see if we can get that sorted and go from there.

 

[zonkerbd]

Sorry, I had already de-soldered all the connections to the switch I just tested connectivity with all combinations of paired connections and switch positions. I've attached a drawing of the a table of results, if that's useful.

 

[RTally]

Sorry, I had already de-soldered all the connections to the switch I just tested connectivity with all combinations of paired connections and switch positions. I've attached a drawing of the a table of results, if that's useful.

Your drawing was really confusing to me. It took me a moment to figure out what you meant by the Os and 1s. Normally, continuity between contacts is indicated as Closed, and an open circuit is indicated as Open. You will notice that the toggle position is opposite the closed contacts. That is, with the toggle pointing down in your drawing, the top two terminals are closed.

The switch is a standard SPDT (single pole, double throw) On-Off-On switch. It has a center position that is considered off, that is, both contacts (1, 2 and 2, 3) are open.

https://www.littelfuse.com/technica...ehicle-technical-center/poles-and-throws.aspx

The KLH schematic can be confusing because it looks like the switch has four terminals. The dot on the schematic next to Decrease and with the arrow pointing to it is there only to indicate the Off position of the switch. That dot does not represent a terminal on the switch. The switch's Off position is labeled as Decrease on the speaker rear. The center terminal on the switch (2) is shown on the schematic as the dot at the other end of the arrow, that is, the dot closest to the tweeter. The arrow on the schematic represents the wiper in the switch.

The tweeter crossover is somewhat complex and not typical of other speakers. The switch changes both the tweeter attenuation and the crossover points.

In the Normal position, the 7.5 ohm resistor is shorted and the two 2uF caps and 3 ohm resistors form a contour network to shape the tweeter's frequency response. With the switch in the Decrease position, the tweeter is attenuated by the 7.5 ohm resistor and the contour network remains the same as in the Normal position. With the switch in the Increase position, one 2 uF cap and one 3 ohm resistor is directly in series with the tweeter and the other 2uf cap and the other resistors modify that part of the contour circuit.

 

[zonkerbd]

RTally, thanks for fighting through my diagram with bad terminology, and for your detailed explanations of the switch and the schematic (good to know it’s a standard switch, in case it ever needs to be replaced). I think I now fully understand the switch, I was clearly confused before.

And regarding the schematic, your explanation helped a bit but I must admit I don’t have a good understanding of speaker crossover networks and how the current flows through the network. Based on your explanations and some of my photos of the older speaker that show some of the switch connections, I drew a diagram of how I think the switch should be connected. Your review would be appreciated.

 

[zonkerbd]

RTally, thanks for the “like” of the diagram.

At the risk of belaboring this topic, I scanned back through my camera roll, and I was able to find a couple of photos of the newer speaker crossover that pinpoints my confusion. Both speakers seem to have identical connections to the switch except for one difference, the connection to the middle terminal on the switch. In the older speaker (oil caps), a 3ohm resistor has one end connected to the middle terminal; in the newer speaker, the 7.5ohm resistor has one end connected to the middle terminal. (In the attached photos, the first photo is the older (oil cap) speaker, and the 2nd & 3rd photos are from the newer speaker. These 2 photos of the newer speaker might not seem totally conclusive that the 7.5ohm resistor connects to the middle terminal, but piecing together these two and others I dug up confirm this to be the case.)

I have to believe that one of these speakers was wired incorrectly, as these different wirings must produce different results? I can’t imagine that the difference in material of the caps (but equal valued) would warrant these different wirings? Tweeters are also identical.

Thanks for any thoughts, e.g., do these different wirings matter, and if so which is correct?

 

[RTally]

What you sketched out yesterday was a wiring diagram, which is a drawing showing how the circuit is wired, that is, what component is physically connected to what.

I ignore wiring diagrams because they can vary without impacting the circuit.

What I use are schematics, which symbolically show the components and how they are connected electrically, not physically. Schematics are not the same as wiring diagrams. A schematic is what is generally used for circuit analysis.

So, to answer today's question you need to draw a schematic of the circuit, something like in post #2. That will tell you if the circuit is the same. If the crossover was mis-wired by swapping a 3 ohm resistor with the 7.5 ohm resistor, the schematic will show the actual circuit and then you can figure out the impact.

 

[zonkerbd]

Got it. Thanks for your patience. I'll do some reading up on how to map a crossover schematic to the actual diagram of the physical layout.

 

[zonkerbd]

Wanted to give an update on progress, and ask for suggestions on my next step.

First, with helpful explanations from members on the schematic and switch, and learning more about how to map crossover schematics to wiring diagrams (e.g., this simple description was helpful: http://speakerdesignworks.com/nodal_analysis.html), I’ve determined the correct wiring for the KLH according to the schematic, with the Normal setting putting 6 ohms in series with the Tweeter; so the 7.5ohm resistor should be connected to the middle terminal, not the 3ohm resistor as was the case with the speaker with the oil caps. Weird. It was either mis-wired, or they changed the spec after abandoning the oil caps.

In any case, I’ve completed the first phase of recapping of both speakers, full recap of one speaker, and leaving in the 8uF oil cap in the other speaker, hoping it would still perform well. Unfortunately, it doesn’t sound nearly as good as the fully recapped speaker, so the oil cap will have to go.

I’ve stuffed back the insulation in the fully recapped speaker, and it sounds very good! I think the base could be tighter, but I haven’t decided yet whether I want to replace the grille cloth and build a grille frame in order to seal the surrounds. To seal the back plate, I decided to use some leftover foam gasket that I used for sealing the woofers in my AR4x’s (after scraping out all that plumbers putty). The gasket compresses down so as not to stick out much and seems to provide a nice seal. I also replaced the nails with some hex socket head wood screws that work well. [Photo attached]

SUGGESTIONS WELCOME
So the next challenge is to figure out how to replace the 8uF oil cap. With the first speaker, the cap was attached with wire nuts to the leads from the drivers. My daughter was able to fit both her small hands into the square hole (one hand at a time), and unwire the wire nuts, and rewire with wire nuts a long extension wire so that I could solder on the new cap outside the speaker cabinet. Unfortunately this method won’t work with the oil cap. As you can see in the photo, the leads are soldered to the cap. If I cut the leads at the solder joint, the wire ends will need to be stripped in order to wire nut an extension as before. But I don’t know that my daughter will be able to successfully strip a wire inside the cabinet. And especially with that short red wire to the tweeter, there is not much wire to work with. Another idea is to try to get my soldering iron in there to solder an extension wire onto the existing soldering joint on the cap, and then cut the terminals below the solder joint.

Ideas / opinions welcome.

 

[zonkerbd]

Here's a photo showing the backside of the plate and the gasket material.

 

[RxDx]

If each wire going to the oil cap has a wire nut on the other end, just
replace the cap and the wires, too

 

[RTally]

Wanted to give an update on progress, and ask for suggestions on my next step.

First, with helpful explanations from members on the schematic and switch, and learning more about how to map crossover schematics to wiring diagrams (e.g., this simple description was helpful: http://speakerdesignworks.com/nodal_analysis.html), I’ve determined the correct wiring for the KLH according to the schematic, with the Normal setting putting 6 ohms in series with the Tweeter; so the 7.5ohm resistor should be connected to the middle terminal, not the 3ohm resistor as was the case with the speaker with the oil caps. Weird. It was either mis-wired, or they changed the spec after abandoning the oil caps.

In any case, I’ve completed the first phase of recapping of both speakers, full recap of one speaker, and leaving in the 8uF oil cap in the other speaker, hoping it would still perform well. Unfortunately, it doesn’t sound nearly as good as the fully recapped speaker, so the oil cap will have to go.

I’ve stuffed back the insulation in the fully recapped speaker, and it sounds very good! I think the base could be tighter, but I haven’t decided yet whether I want to replace the grille cloth and build a grille frame in order to seal the surrounds. To seal the back plate, I decided to use some leftover foam gasket that I used for sealing the woofers in my AR4x’s (after scraping out all that plumbers putty). The gasket compresses down so as not to stick out much and seems to provide a nice seal. I also replaced the nails with some hex socket head wood screws that work well. [Photo attached]

SUGGESTIONS WELCOME
So the next challenge is to figure out how to replace the 8uF oil cap. With the first speaker, the cap was attached with wire nuts to the leads from the drivers. My daughter was able to fit both her small hands into the square hole (one hand at a time), and unwire the wire nuts, and rewire with wire nuts a long extension wire so that I could solder on the new cap outside the speaker cabinet. Unfortunately this method won’t work with the oil cap. As you can see in the photo, the leads are soldered to the cap. If I cut the leads at the solder joint, the wire ends will need to be stripped in order to wire nut an extension as before. But I don’t know that my daughter will be able to successfully strip a wire inside the cabinet. And especially with that short red wire to the tweeter, there is not much wire to work with. Another idea is to try to get my soldering iron in there to solder an extension wire onto the existing soldering joint on the cap, and then cut the terminals below the solder joint.

Ideas / opinions welcome.

Good job!

As for the oil cap, I would leave it in place and solder a length of wire to where the red wire is soldered to the oil cap. As for the other terminal of the oil cap, I see two options. 1) Cut the blue wire at the cap, undo the knot of the blue and red wires, and hopefully, the blue wire will reach to where you can strip it and connect it to one end of the cap. 2) The other lead of the oil cap should run to the terminal plate in the back and you can disconnect the oil cap there and connect the new cap to where the blue wired was connected.

 

[alteclipsch]

As much as I would be exasperated by working on these epoxied speakers..... I desire a pair.

 

[RTally]

As much as I would be exasperated by working on these epoxied speakers..... I desire a pair.

I have a pair of 1963 Model Sixes in my pile of speakers to work on. My tweeters have no sound, and I expect it is the caps. I plan on pushing out the baffle to access the internals. I want to save the cloth because it is in good shape.

I am in no hurry to work on this pair because I have a newer pair of Sixes that are connected in my office.