KLH 6's - How do you get inside to repair?

[Guest dbradley]

I posted a question about these speakers yesterday. However, I spent some time working on one of them last night and my original post seems to be in error. The other KLH speakers I own have grills covered with grill cloths and held onto the front of the speaker with velcro. I had heard about earlier models where the grills were glued on, instead of velcroed, and expected that is what these 6's are. However, it now appears that there is no separate grill per se. There is a cloth, which may be held in place by being underneath the protruding outer edges of the speaker. Underneath it is a black foam/cloth and underneath that is (probably at least 1" thick) plywood. I have chipped away at a small corner of the speaker to find this. Unfortunately, the only thing I can think of to do next is to destroy the outer cloth to get inside. It is astonishing to me that KLH would build a speaker where that was the basic method of repair, because if only one speaker broke, they would have to replace the cloths on both of them in order to maintain a match. So I am thinking I'm making a mistake.

Does anyone have experience with a similar vintage of KLH 6?

[Andy]

If you have an early pair of model Six's (approx. serial #30,000 or lower) not only does the grill not come off, but the drivers are epoxy mounted to the baffle board, not screw mounted. So getting inside means prying the cabinet open at it's seams! Kloss even had a U.S. Patent on this system, but I'm not sure anyone would copy this connstruction technique.

[soundminded]

I have some very bad news for you. There is no practical way to get inside early KLH model six loudspeakers to repair them. Mine went back to the factory several times for repair there. In the first instance, they pried the baffleboard out with what appears to be a prybar. You can still see where it was inserted. This was to replace a tweeter. In the second instance they had to replace a bad capacitor. To do it, they had to remove the woofer cone and work through the speaker basket which is epoxied in and then recone the woofer. Model sixes which were made later on were more conventional using removable drivers and grill cloths like normal speakers.

Here are some alternative suggestions. If the woofer still works but the tweeter doesn't, you can acquire another tweeter and mount it along with substitute crossover components externally to the woofer. It's the same tweeter as in the Model 5, 17, 12 and a few others. You can also experiment with other tweeters or tweeter midrange combinations but you will not exactly duplicte the original sound. The other possibility is to use a reciprocating saw to cut away the back. leave enough room around the edges to attach an overlapping piece of wood which can attach to the original box. It is a shame that among Henry Kloss' talents, practical manufacturing to facilitate repair was not one of them. What was this man thinking...or did he give it any thought at all?

Good luck.

[Andy]

I'm keeping my fingers crossed on my 1958 model six's which are working perfectly.......But, I've been thinking of options when I need to get inside the cabinet.

As Soundminded says, "cut a hole in the back to access wiring, crossover, etc." I think a hole with a 45 degree beveled edge makes sense so the revoved piece will fit snugly in place when done. But, you still would not be able to remove the drivers unles a similar technique is used on the baffleboard.

What a shame, I never thought I'd be advocating putting a saw to a piece of hifi history and I'm not sure I could do it, my model Six's are among the first made (#'s 0684 & 0711)...are the 15 ply marine plywood-Korina blond finish which KLH used in 1957-59, and I consider them pices of art!

[Guest dbradley]

To Soundminded and Andy - Thank you both for your responses. I posted my first group of questions before I pulled up the archives in the forum and read a number of earlier posts from each of you and learned more about this situation. A number of the earlier posts from others as well talk about the early versions of the 6's being worse than the later ones and mentioned dividing lines like serial numbers of 30000 or under. Interestingly, the serial numbers on mine are 83980 and 84000. I don't know if that will mean the drivers are not epoxied in? But the lack of a true grill is certainly an issue. I also saw posts indicating that the tweeter problem is more often the capacitors than the tweeters themselves. My 6's have the double posts on the back, linked with a removable coupler. If I remove the coupler, I can drive either the woofer or the tweeter separately. I tried that and found that I could get sound out of the tweeter when I turned the volume up very high. I don't know if that has an implication for whether the problem is the caps or the tweeters?

I am thinking about this approach. What I have done so far has not destroyed the grill cloth irreparably. What if I drilled a couple of small holes together on the back of each speaker along the seam between the back and sidewalls, and took a sabre saw and cut out the entire back in one piece. Presumably then I could access everything. If the problem is the capacitors, I ought to be able to get to them, right? If the problem winds up being the tweeter, if it was epoxied in, I probably had to destroy it anyhow in attempting to remove it. The bad news would be if 1), it is the tweeter and 2) they are screwed in, in which case I will still have to remove the baffleboard, but I can presumably crowbar that out from the rear as easily as from the front and make no marks that would be visible when the whole thing is back together. When I replace the back, I can use woodputty, which dries like wood, and even caulk it to ensure the seam is airtight. How does that sound?

[soundminded]

Were I confronted with this problem (and this could happen), I think what I'd do also is to cut out the back at least an inch or two from the edge. I'd buy some 2" or 3" wide aluminium plate and some 2" or 3" wide rubber and reattach the back around the opening by having the plate and rubber form an air tight piece straddling the opening. The good news is that the plywood should hold wood screws very securely and the back could be removed later on if I ever had to get inside again. Having used this kind of material for other purposes before, I found it inexpensive and easy to work with. Good luck.

[Andy]

Here's a pair that has an epoxied woofer and a screw mounted tweeter? ebay number 5869990959. These have serial numbers of 73,000.....so it looks like KLH did make more bonded speakers then I thought. I think the change-over happened in about 1965 when the model 17 & 20 was introduced. Production volume was increasing rapidly after Singer bought KLH in 1964 and Kloss's epoxied drivers were to much of a service nightmare.

[Guest dbradley]

To Soundminded and Andy - Thank you very much for your research and thoughts. You guys are both great. Scary to hear that a 73000 serial number still had an epoxied woofer, given that mine are 84000 - pretty close. I have one other person who I met through this forum who has been encouraging me in emails to cut out the front cloth on the expectation that the woofer will be screwed in but the chances of that just dropped. I like the thought, if I have to open up the back anyway, of doing it with a beveled cut and making re-entry easier since these are after all almost 40 year old speakers and the need for subsequent repairs of other parts certainly could occur. My original focus had been on minimizing the impact on the appearance of the speakers, because the cabinets themselves are walnut veneer with little in the way of dings and no crushed corners. I expect after sanding and oiling, they will really LOOK great. But it doesn't matter if I can't get them to SOUND great as well. And messing up the back is not as big a deal.

So I have a decision to make - removing the front cloth vs. opening up the back. If I open up the back, I will do it following the suggestions both of you have made. I'm going to see if I can even more insight into serial numbers at or above 84000. If not, sounds like a coin toss.

Thanks again for your help.

[Carlspeak]

Hi Dave.

I had an idea for a different approach to getting into those model sixes. Unfortunately, I can't try it on the one bad one you didn't take. It's gone now (picked up yesterday with the trash).

The idea goes like this. First, it's based on the assumption that the epoxied drivers are attached to the baffle board BEFORE it is installed hopefully via gluing into the cabinet along with the grill cloth. I don't remember seeing any screws holding the baffle board in place. Thus, it must be glued in.

Secondly, the next assumption is that the outer cabinet trim at the front of the speaker box is not any narrower than the baffle board because if it works, the baffle board will be pulled directly out from where it sits now. This idea will also damage the grill cloth, but you can probably access more from Dale who posts here regularly.

You buy some long lag bolts at least 1/4 inch in diameter and a 2 inch square piece of hardwood long enough to cut it into two lengths that are longer than the width of the speaker box. Thread the lag bolts into the hardwood in two places on each piece near the inside edge of the baffle board width. Pre-drill 4 carefully located pilot holes for the lag bolts thru the grill cloth into the baffle board taking care to keep them away from the drivers. Now place the hardwood pieces across the face of the speaker front with protective materials under them so they don't damage the cabinet wood facing and gradually thread the bolts into the drilled holes. Obviously, the holes in the baffle board must match the holes in the hardwood.

Leave enough slack in the lag bolts so they anchor themselves well into the baffle board BEFORE they bottom out on top of the hardwood. Steel washers are suggested under the lag bolt heads.

Once the lag bolts bottom out they will start to pull on the baffle board with great force. If my theory holds true the baffle board should become unglued from the cabinet innards.

Let the folks here know if you try this and how it worked out.

Carl

Carl's Custom Loudspeakers

[Carlspeak]

Here's another idea worth consideration.

Instead of trying to salvage the tweeter and/or the crossover, buy a new tweeter and mount it to the top of box (ala the B&W Matrix 801 approach). They have proven a tweeter of this type images excellently and has little if any diffraction issues.

Parts Express sells one that is designed to do this (part no. 297-409). Buy a two way crossover that crosses at 3000 hz and mount it to the back of the speaker. Run wires from the original connector posts to the crossover and wires to the new tweeter. Do not use the low pass section of the new crossover. That will be taken care of internally.

I think those old tweeters aren't worth salvaging anyway. New dome tweeter designs offer so much more detail and imaging.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[tysontom]

Most problems with KLH Sixes (and Fours) seems to be crossover capacitors. In the case of the Six, the 8 mfd cap can go bad if it is the paper-type capacitor. The earliest oil-type capacitors rarely gave trouble, I believe, because they were usually

mil-spec war-surplus items. The tweeter can be okay, but little or no sound will eminate from the speaker. Part of the crossover is attached to the front baffle board, which is also glued to the speaker cabinet.

As others have noted, these early model Sixes have the epoxied woofers and tweeters (although at some point KLH began putting in tweeters with replaceable, flange-type tweeters with ceramic-type magnets). There was no grill-cloth frame or panel; the grill was stretched across the front baffle with a black cloth underneath to hide the drivers. This grill cloth material was tucked around the edges and glued or fastened on the backside of the baffle board in some cases, or permanently attached into a small groove along the edges of the baffle. It is about impossible to remove the grill without damaging it; at the factory I understand that workers simply cut the grill away, ripped out the woofer cone and coil assembly, and made any internal repairs through the woofer hole, then put in a new woofer cone, voice coil, spider and assembly and glued it back together with a new grill. The intensity of labor to do this would have been draconion.

http://www.classicspeakerpages.net/dc/user_files/1059.jpg

KLH Six Epoxied Woofer (back-side view)

http://www.classicspeakerpages.net/dc/user_files/1061.jpg

KLH Six Epoxied Woofer (front-side view)

It's hard to imagine how Henry Kloss decided on this method of assembly. It is at the same time both ingenious and crude. It is a reflection of Kloss' great innovation and imagination, yet shows a less-than-rigorous design and engineering style. While it is true that KLH got great consistency with voice-coil alignment and so forth (due to the alignment jigs that were his actual patent), the problem of repairing one of these speakers would seem to outweigh the advantages of the jig. Service costs for KLH must have been horrendous. Nevertheless, KLH made a great number of these epoxy speakers, including many KLH Sixes, KLH Fours and KLH Sevens, and many have begun to give problems.

--Tom Tyson

[soundminded]

"It's hard to imagine how Henry Kloss decided on this method of

assembly. It is at the same time both ingenious and crude.

It is a reflection of Kloss' great innovation and imagination,

yet shows a less-than-rigorous design and engineering style."

Tom, you have a remarkable talent for understatement. :-)

[tysontom]

>It is a shame that among Henry Kloss' talents, practical manufacturing to facilitate repair was not one of them. What was this man thinking...or did he give it any thought at all?

Soundminded, you're not too bad yourself at understatement!

--Tom Tyson

[Guest dbradley]

Tom - Thank you very much for your reply. After I posted, I spent some time reading the archives on this site related to the KLH 6's and read many of the posts you have made in the past, which were very helpful to me in coming to understand the problem I face.

I have two questions: 1) You stated that part of the crossover is attached to the front baffleboard. Does that mean that it is attached to the front of the baffleboard, so that I could only access it by removing the grillcloths, or does it mean that it is attached to the rear of the (front) baffleboard, so that by opening up the speaker from the rear, I would be able to access it? 2) Do you have any idea where the capacitors, crossovers, etc. are? If they are in the back, are they closer to the woofer or closer to the tweeter, or mounted on the side or mounted on the rear wall? I'm asking these questions because, unless there are important reasons to open up the front, I am inclined to assume, at first, that the problem is with the caps, etc. rather than the tweeter and cut open the back to access them. I'm trying to avoid damaging them in that process, and trying to position the opening in the best location.

Thanks for your help.

[tysontom]

dbradley,

The tweeter capacitor is attached to the inside of the front baffle board, or the board on which the woofer and tweeter are mounted. See Fig. 1 below:

http://www.classicspeakerpages.net/dc/user_files/1071.jpg

Fig. 1 KLH Six early versions showing oil-filled and paper capacitor (from eBay post)

It is possible that part of the crossover is on the terminal board, perhaps across the switch, as there are *three* capacitors shown in the early KLH Six crossover diagram, but it is possible that the crossover on the front board is a multi-value device.

Nevertheless, if you feel that the drivers are okay, I would make entrance into the *back* of the speaker. You could cut a hole, perhaps 10" x 10" (or even 10" x 15" for that matter that would also include the terminal strip), that would allow you to gain access into the speaker, remove fiberglass to get to the job, and so forth. Once you have the panel removed, you could then glue some furring strips inside the cabinet against which the panel could be re-inserted, or you could install a flange on the outside of the panel with a gasket to then re-attach to the cabinet when finished.

--Tom Tyson

[Guest dbradley]

Tom - Thanks again very much. A picture is worth a thousand words, although you described it clearly.

I don't know for a fact what the problem is. The archival posts on this website indicate that the caps are more often the problem than the tweeter itself.

The only other "evidence" I have is from the fact that, as you know, the speakers have multiple posts on the back that allow the tweeter and woofer to be driven separately. When I tried driving the tweeters, I could get some soft sound out of them both, driving them at high volume. Again, the archival posts say that tends to imply a problem with the capacitors. Also, it's interesting that both speakers have the identical problem. The good news is that the woofers on both speakers sound fine to me. I'm assuming they are epoxied in, rather than screwed in.

So that's where I'm heading at this point. If it is not what you would do given the same information, let me know. Probably won't be able to get to the job for another week or so anyhow.

Dave Bradley

[Carlspeak]

Hi Dave. Carl again.

It looks to me from Tom's pictures of the baffle boards like jacking the baffle board as I suggested earlier is the way to go. It's readily apparent that whomever was selling them on e-bay apparently succeded in removing them somehow. Also, most of the xover components appear to be attached to it which makes it that much easier to work on it once you remove the baffle board.

Perhaps a few readers of these posts who have conducted 'surgery' on the early KLH 6's could share their experiences?

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[tysontom]

>Tom - Thanks again very much. A picture is worth a thousand

>words, although you described it clearly.

>

>I don't know for a fact what the problem is. The archival

>posts on this website indicate that the caps are more often

>the problem than the tweeter itself.

>

>The only other "evidence" I have is from the fact

>that, as you know, the speakers have multiple posts on the

>back that allow the tweeter and woofer to be driven

>separately. When I tried driving the tweeters, I could get

>some soft sound out of them both, driving them at high volume.

>Again, the archival posts say that tends to imply a problem

>with the capacitors. Also, it's interesting that both speakers

>have the identical problem. The good news is that the woofers

>on both speakers sound fine to me. I'm assuming they are

>epoxied in, rather than screwed in.

>

>So that's where I'm heading at this point. If it is not what

>you would do given the same information, let me know. Probably

>won't be able to get to the job for another week or so anyhow.

>

>

>Dave Bradley

Dave, from what you describe you definitely have a bad crossover -- a really common problem for KLHs. Carl may be right about jacking out the baffle board, but I am not sure how KLH glued that board to the rest of the cabinet. I know it is held in there very securely with probably some sort of wood glue or epoxy glue, so you might have to be very careful not to splinter the baffle. As am aside, some early AR-1/AR-3 cabinets contained a groove that was routed in the side boards, and the baffle was epoxied to that, flush with the front (before application of the molding pieces). Jacking out the AR front baffle would tear that cabinet all to pieces, I believe, but the KLH may indeed be quite different. The KLH Sixes in my picture were sawed in half and the cabinet stripped away from the baffle. If your grill is still okay, then you have to sacrifice it, too if you break out the front, because there is no "removing" the grill on that version of the KLH Six; it has to be cut away and removed from the edges because there is no frame as in later versions.

The reason I mention going into the back is that I have seen that done by a friend with KLH Sevens, and it worked well for him. He started by drilling a hole, then used a jigsaw or Sawzall and cut a fairly neat square hole on the back. He then made a flange around the back that he could re-install on the speaker to make it air-tight again. Another consideration: you will probably need to get some butyl-rubber, such as Lords BL100, and dilute it (50-50) with water and apply it to the woofer surrounds of the early KLHs. Every one I've seen has dried out and leaks through the surround.

--Tom Tyson

[Guest dbradley]

Tom - Thanks again for your advice. You've given me confidence that the problem is the crossovers, which is what I needed. I will go in from the back, as you suggested, and use the rubber/metal flange device to reseal it, which is what someone else suggested to me as well, even though it won't be pretty, because that will make access the next time, if necessary, much easier. I will see what the woofers look like and look for the butyl rubber compound if they are dried out, as you predict. Thanks again - I'll let you know how it turns out. You have been a great help.

[Guest dbradley]

Tom and others - I sawed open the backs. I created a rectangular hole about 12"x18" with the posts/frequency adjustment plate in the center. I started the process by drilling a couple of small holes to let my sabre saw blade in and both driulled and sawed on a 45 degree inward slant, so that when I place the sawed out portion back in, it does not fall in but fits in and stops. There were some sort of capacitors on the rear of the posts, wired to the rest of the electronics which were on the rear of the baffle board facing me from the back. The speakers (Serial no's 84000 roughly) had oil-filled caps. I took them to my repair guy who just left me a message that the caps were bad, the tweeters are fine, he has replaced the caps and the speakers sound great. Of course, the surgery willl leave them looking less than great from the rear, which might be a problem for others if I were selling them (which I don't plan to do). Cutting them open removed a good 1/8" of wood since the backs are a low-grade plywood. I plan to reseal them using a technique a friend suggested, which is to place a piece of rubber (like you would fine on the bottom of a garage door) across the openings, cover it with a piece of metal with screw holes down both sides and screw it into both the speaker and the piece I sawed out to create a seal.

Thanks again for your advice, pictures, etc. Hopefully I will have restored the sound of a great pair of speakers. If I have, I will sand and reoil the walnut veneer, which was actually in pretty good shape - no dents, banged corners or holes, just stained and uneven color.

Dave

[Guest dbradley]

Picked up the speakers last night. Want to correct one mistake I made. Although the caps that were bad looked just like the pictures of the oil-filled caps I have seen, they were not the oil-filled ones. Three out of the four dual caps (in the two speakers) were completely shot out of both wires and all four were replaced. So this problem is exactly what I have read in so many of the earlier posts.

Interestingly, the woofers have retained their flexibility, and since my repair will allow me to easily reopen them at any time, I'm not going to apply any of the coatings that have been suggested since they do not currently seem to need it despite being 40 years old!

Thanks again for the advice, everyone - especially Tom.