A (nearly) full KLH Model Four restoration guide

nickdinatale

Active Member
Close to a year and a half ago I purchased my first pair of KLH Model Fours. They were in working order, but not perfect cosmetically. I had read all I could find on AK, as well as the rest of the internet, so I already knew that they were pretty well-regarded, and semi-rare. I was in the midst of collecting pretty much every 60s to early 70s KLH that I could scoop up for a reasonable price. Needless to say, I was pretty excited to finally get my hands on a pair of Fours.

Originally a direct competitor to the AR-3, the KLH Four definitely lost the competition as far as popularity. The highest Model Four serial that I have come across is number 7434 (which I believe was on the auction site), while the AR-3 and 3a made it into the 90k range, and were produced into 1976. Price points for each were about the same - the KLH Four retailed from $209 (utility cabinets) to $231 (walnut) in 1960. The Model Four was also eclipsed by the massive popularity of the KLH Model Six, which debuted the same year, but was nearly half the price. Nevertheless, the KLH Model Four found an audience at CBS Records, serving as their monitor speakers, according to Henry Kloss in a 1996 interview.

klh four at cbs.jpg

Note that the forum I found this in references these as “upside down Model Sixes,” but the Model Four had the badges located in the upper right, so I’m guessing that these are in fact Model Fours being used.

Upon listening to the Model Fours for the first time, I was pretty happy with them. They were pretty laid back, but still very musical for having 50+ year old capacitors inside. I was very content and didn’t intend to recap them right away. Some time passed, and eventually I realized that they just weren’t pulling their weight, so I set them aside as a future project to undertake.

That time finally came last July, as my childhood dog, Kasey, became ill, and I spent a month living at my parents in order to spend time with her. I wanted my dad’s help with these anyway, and also wanted more room to work on them, as I already knew they would be a very involved restoration. The distraction was also a welcome bonus for both of us, I think.

Originally, I set out to restore the speakers via a recap, new surround sealer, and a cabinet refinish. As an added bonus, I wanted to do it without having to destroy the original grill cloth. I removed the rear plate that covers the hole where the crossovers are suspended and began lightly chiseling away at the epoxy. (Note: don’t lose the black rubber grommets that insulate the A,B, and C terminals!) The epoxy crumbles pretty easily, so it didn’t take all that much force to work through it. If you’re giving this a go yourself, the main key is to take your time and be careful to not damage the crossover, particularly the inductor, which has bare copper wire that is quite thin. Stay toward the edges if possible.

1_Chiseling crossover.jpg

If a recap is all you’re trying to do, you can access the double 2uf capacitor (pictured) and replace it. The 3uf cap is mounted on the rear panel of the cabinet, just off to the side of the crossover. (See two photos ahead). You may be able to reach in and remove it, or at least clip the leads. Make note of which color wires are connected where so that you can reference the schematic (included later). It’s also a good idea to label each cabinet and crossover with the serial it belongs to in order to keep things separate. Taking a photo to note the orientation of your switches to the plate is also crucial for reinstallation.

Our next step was to open up the rear panels. We laid out even edges along the back of the cabinets and marked them with masking tape for cut lines. At the time we didn’t know how thick the cabinets were, so we made plunge cuts with a circular saw. (The answer is 3/4”). From there, we used a jigsaw to get the corners. Even having laid everything out, the cuts weren’t perfectly straight, so just take your time and do the best you can.

2_Dave cutting.jpg

3_Back panel removed.jpg

After removing the rear panel, the familiar sight of pink fiberglass insulation appears. Underneath the insulation lies the front driver board. Notice the thin black cloth covering the woofer - this is important. As the woofers aren’t built into basket frames, the black cloth is stapled down in a very taught manner in order to protect the woofer’s cone from encountering any interference from the insulation pressing against it. (More on this later). At this point in time, I was still hoping to save the grill cloth. (Notice it peeking around the corners of the front board).

4_KLH Four innards.jpg

Unfortunately, I soon realized that the grill cloth was doomed to be ripped off. We actually removed the entire front driver board from the cabinet completely, thinking it would allow for removal of the cloth. This wasn’t the case, as the cloth was both stapled down, and then the front panel was glued and seated, sandwiching it in between. As we removed the panel, the cloth was ruined. From there, I removed it from the front panel and then had to tediously chisel it away from the main cabinet, and from the edges of the driver board in order to allow for a clean seating of the panel back into the cabinet.

5_Chiseling grill cloth.jpg

Inside of each cabinet there were even stamps from when they were built. Mine were in red and said “Denny May 1964 Roll” and “Denny June 1964 Roll” respectively.

6_Inner build stamp.jpg

(cont.)
 
At this stage of the restoration, I went ahead and sanded down the cabinets. Generally I don’t completely sand out speaker cabinets and go the Howard’s RAF route, but these cabinets had some deep gouges I wanted to remove. I mostly used a palm sander.

7_Sanded cabinets.jpg

I did a bit of linseed oil on the cabinets but then (with my dad’s advice) decided to hold off on finishing them fully. We then installed an inner lip on the rear opening of the cabinets to seat the back panel on. For this, we used four cuts of 2” x 1/4” plywood slats (IIRC) on each cabinet. We countersunk around 10 holes all around the edges, laid down a thick layer of wood glue on each slat, and drilled them in. (Look further on in the post for a photo of the inner lip).

At this point in the project, Kasey passed away and I lost interest for a while.

kasey smiling.JPG

Winter is coming up here though, so I had to get the cabinets inside in case of water leakage from snow. This prompted me to finally get them done. Per suggestion from another Model Four restoration thread, we made up plates identical in size to the original ones to mount underneath and support the crossover. After spending some time with the drill press and drilling out holes to match, I was ready to rebuild the crossovers. At my dad’s suggestion—he’s good at pointing me in the correct direction—we worked out a complete schematic before I started replacing components.

klh model four schematic_revised.jpg
(Edit: this schematic is a revised version that I posted on 11/28/2018. Read thread for more details on this.)

Once the new caps (Mundorf MCap Classics) were installed, I also touched up a few of the other solder joints that were becoming brittle. My next step was to reattach the crossovers to the plates. I passed all of the leads through the hole where the epoxied crossover was, and then started mounting to the plate, while making sure to insulate the terminals via the six black rubber grommets that originally separated them. With the thicker profile of the plates compared to the original, I was worried about shorting if anything were to loosen up. To protect the portions of the screws that pass through the plate, I added a few wraps of electrical tape. Upon finishing, I used a meter to double check my work.

8_Assembled crossover.jpg


We used a thick bead of silicon to re-adhere the front panel and ensure a good seal on the cabinet then drove finish nails back into the four original holes where they were before.

9_Silicon front panel.jpg


The last main step was to lay out, countersink, and screw the back panel to the inner lip we created before. Pretty straight forward.

10_Rear panel layout.jpg

As I mentioned earlier, the fabric that protects the woofer cone is very important to proper function, as well as the safety of the voice coil. It’s worth it to make sure it’s taught to avoid having to do more repairs. If you need to add new cloth, don’t be shy on the number of staples you use (the original builders certainly weren’t). Note that in one of my speakers where I couldn’t reuse the original cloth, I cut up an old, thin shirt.

11_Packed cabinet.jpg

12_Screws in rear panel.jpg

I’m not 100% done with this project yet, but I now have the speakers hooked up and they sound great so far. I’m planning to unscrew the rear panel, and add silicon around the inner lip for a correct acoustic seal (I just want to be SURE that I’m done inside the cabinets. Once that’s done, I’ll make a small seal (maybe some form of rubber gasket) around the crossover hole. Then just some new surround sealer, and these should be ready to go for another 50 years. I also want to make new grill cloths for them, but that’s lower on the priority list.

Hopefully this thread can be of some help to others with Model Fours! They’re really fantastic speakers and well worth the involved restoration.

Links to sources that I cited in this post, and that are interesting on their own:

http://www.classicspeakerpages.net/...652-uncle-titos-beloved-klh-model-4-speakers/
http://www.aphenos.net/electronics/speakers/klh/all_klh.htm
http://www.classicspeakerpages.net/IP.Board/index.php?/topic/2517-klh-model-four/
http://forums.stevehoffman.tv/threa...street-studio-nyc-many-pictures.388186/page-6
 
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Added bonus: what looks to be a Model Four up on the wall behind Bob Dylan in ~1965. No badge on the speaker though.
bob dylan_klh model four.jpg
 
Great..... looks really good!

About to do a repair on a set of Cerwin Vega AT 8s.. not as intense as your recovery just some foam damage and minor cabinet fix.

I always re-insulate the cabinets as I have found that most lack proper damping.

Looking forward to firing them up at full throttle to hear what gives CVs their "calling" ;)
 
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Sorry for your loss. The crossover diagram and the layout of my Fours seem about the same but like the diagram of my 17s I cannot figure out what Henry Kloss was doing. Did you get the surrounds resealed? No pics of the front.
 
Yes indeed. Thanks for the crossover schematic.
It may actually be the only one around. I know I couldn't find one awhile back.

I cannot figure out what Henry Kloss was doing

Seems strange to me as well.
Really? The tweeters are run in series with two switches on them? For two different frequency adjustments?
Why not just run them in parallel, switch each separately, and effectively have a three-way.
 
Mine were in red and said “Denny May 1964 Roll” and “Denny June 1964 Roll” respectively.
Denny Roll was also responsible for constructing the cabinets of my AR-4's from June 1964.

This is a great thread, and I don't quite understand how those switches work either. Also, I don't follow why the front panel required removal unless it was for re-doping woofer surrounds. This was a stated objective, but we don't see it here.

Very sad to hear about Kasey. :(

denny roll stamp 1964.jpg
 
Dang, I've got a pair of the later Fours that are waiting for some restoration attention. Nice work and thank you for your time and effort!

Biggles
 
I always re-insulate the cabinets as I have found that most lack proper damping.

That's something I hadn't even thought of! Maybe I'll have to do that before fully sealing the rear panel. Good luck with your restoration!

Did you get the surrounds resealed? No pics of the front.
Also, I don't follow why the front panel required removal unless it was for re-doping woofer surrounds. This was a stated objective, but we don't see it here.
View attachment 1329579

I'll add front pictures soon. Haven't put the sealer on yet as I want to finish 100% with the cabinets so that nothing sticks to the sealant. Removing the front panels was a mistake that came from trying to save the grill cloth. I definitely don't recommend doing so if it can be avoided!

Denny Roll was also responsible for constructing the cabinets of my AR-4's from June 1964.
View attachment 1329579

Woah, this is quite interesting. I'm wondering if Henry Kloss just kept the same supplier of cabinets when he started KLH?


Sorry for your loss.
Very sad to hear about Kasey. :(
View attachment 1329579

Thank you both. She was a great dog and is definitely off chasing squirrels somewhere else now.
 
Trying to work with the schematic... Would it be possible to get the
switches diagrammed? I'd think they'd have a 4th connection, supply
in or out, like the Model Six.

KLH6xo.jpg

I will confess, I am too lazy to open mine up!
 
I have one set of KLH Sixes with "Denny Roll 1963" stamped in them. I have another set of even earlier Sixes with Oil caps with nothing stamped inside.

Nice thread. Thanks for the diagram. That's a great contribution.

I'll keep my eyes open for a set of Fours. I have Fishers that can drive 16 ohm speakers such as the Fours.
 
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Terrific write up and photo documentation.
"Denny Roll" was stamped inside many speaker cabinets. Both AR & KLH used the same cabinet manufacturer.
The model Four was manufactured from 1958-64. The model Six from 1958-72. Cabs are different sizes, so the later removable grill from Six's will be smaller.
 
Photos of the fronts!

The tweeter housed inside of the black plate on the first cabinet is the same as the other three. The only actual difference is the black plate itself, and a larger hole around that tweeter. I'm guessing this was a factory job - either done before the speaker even left the factory, or a replacement soon after. I didn't see any date codes on any of the drivers.
L1009536.jpg L1009540.jpg
 
Updated the schematic to denote switch positions. Also used Photoshop to flip around switch positions and choke so that they make sense with the orientation of the plates for less confusion. Going to delete the older schematic I had uploaded in order to keep things consistent.

I wasn't sure how to best add details on the choke. I measured resistance between the middle terminal of SW2 (where the tweeters connect to SW2) and the top terminal (where SW2 connects to SW1). Here are my readings:

With SW2 in "NORMAL" position: 0.8ohms
With SW2 in "DECREASE" position: 1.4ohms
With SW2 in "INCREASE" position: 0.2ohms

klh model four schematic_revised.jpg
 
I also finished sealing up the cabinets today. Took the screws on the rear panel out and put a bead of silicon in, then went around the hole where the crossovers sit with AR surround putty from Vintage AR. Opted for the putty on the crossover plate for ease of access in the future. If anyone else tries this, I'd say that you could go a bit thinner on the putty than I did (my rear plates have a bit of a "bump" in the center). After placing the putty, I just weaseled the crossover back through, gave it a firm pressing down, and reused the original finish nails to snug everything up.

IMG_7034.jpeg
IMG_7040.jpeg

After finishing with sealing the cabinets on the back, I'm now in the process of using surround sealant on the cloth surrounds. I did one already (first photo), and the difference is incredible. I've heard the difference on several sets of ARs in the past, but it's SO noticeable on these Fours. (Side note: the dust caps on my two woofers are a little different - one looks like it has some sort of sealant applied to it while the other doesn't).

IMG_7041.jpg
IMG_7042.jpg
 
Still hard for me to tell how the switches work, so I ad-libbed, like this:

four_xo.jpg
 
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