Jump to content
The Classic Speaker Pages Discussion Forums
JayRd7

Preparing for Model 20 restoration - advice appreciated!

Recommended Posts

Hello all,

I have KLH Model Twenty speakers that I am looking to do a restoration on, but wanted to make sure of a few things before I begin as I've never done anything like this before. 

-When I first purchased the speakers about 15 years ago, they actually came re-capped which was nice, but I'm wondering if anyone recommends upgrading the capacitors even more. Off the top of my head I can't remember what was used for the recap but I think they were pretty cheap caps - I've heard good things about Dayton caps for these speakers and just wondering if it would be worth it. 

-I definitely plan on resealing the surrounds, using the famous RoyC/vintageAR stuff that I've heard so much about and found on eBay. Should I also do the dust caps on these? My biggest question is, how many coats? I've heard not to layer on too thick, just wondering if anyone who's done a restore on these 20s or the similar 17s did one or two coats. 

-I've seen some mention about replacing the foam where the tweeter sits, any specific recommendation on type of foam for this and the procedure for doing so?

-I had the turntable serviced at a local audio repair shop by a guy who used to be an engineer for KLH decades ago. He took a look at my speakers and said that they're in decent shape but need the basics done to them, however, he also said that the cabinet boxes themselves need to be re-glued as they are a bit loose. I haven't found a whole lot on that online, especially for this particular speaker, so wondering if anyone has done this and what it involves, as I wouldn't know where to begin. 

Is there anything else I'm missing that I should consider doing on this restoration? Any help and advice is greatly appreciated!! Thanks everyone! -Jared  

Share this post


Link to post
Share on other sites

Welcome Jared!

So you have the whole Model Twenty--not just the speakers. Nice.

If the speakers were recapped 15 years ago they "should" be fine, assuming the person knew what he was doing. Yes, Dayton poly caps are good and should last forever but even if electrolytics were used they "should" still be OK.

Yes--do the dust caps too. This is what KLH recommended in Service Bulletin 60 (in our Library): http://www.classicspeakerpages.net/library/klh/other/klh_schematicsservice/klh_service_bulletin_60.pdf   Go easy. You want to completely seal the surround (or "skiver" as KLH calls it) with the thinnest coat possible.

The foam behind the tweeter is a gasket but the white foam they used can get flattened. If the tweeters have never been removed it may be OK. If you want to replace it there is nothing magic. You can use the excellent foam gasket from Parts Express but you have to buy a whole lot (if you decide to change the caps it may be worth it because you also use it as the woofer gasket). https://www.parts-express.com/parts-express-speaker-gasketing-tape-1-8-x-3-8-x-50-ft-roll--260-540 You could use Duct Seal frome Lowes or Home Depot's Electrical Dept. It's the same stuff Vintage AR sells and you get a brick of it for about 3 bucks at HD/Lowes  https://www.lowes.com/pd/Gardner-Bender-16-oz-Duct-Seal/4595233 Or go to a craft store like Michaels and get a sheet of craft foam for about $1 and cut your own  https://www.michaels.com/12x18-foam-sheet-by-creatology/M10597609.html

I'm hoping one of the master woodworkers like Glenn or Roger chimes in on the gluing. Pictures would help. You can use old fashioned Hide glue or more modern Carpenter's wood glue but you have to be able to get the glue into the seams and crevices, then clamp everything with big bar clamps. Both of these types clean up with water, so if there is any squeeze-out onto the veneer it can be removed easily.

Anything else? Well I'm assuming the former KLH guy also checked the amp while he was checking the TT. Those old Garrard TTs can be a pain and the amps can need attention but if that was done I'd say you're good to go.

If you decide to change the caps, be sure to use some heat shrink tubing or otherwise ensure the metal leads cannot come in contact with the metal plate (stupid design IMHO). Below is a picture of a 17 xo with Dayton caps. Also below is a pic of woofer removed. You'll have to scrape off the old Mortite and use either the PE foam tape gasket or the Duct Seal.

I'm also attaching a pic of the identical Model Seventeen xo, this one re-capped with yellow Carli caps. In that I moved the caps completely off the metal plate.

Show is some pics. Resize them to about 100KB if you can.

-Kent

 

KLH17new_xover  crimps.jpg

KLH20 woofer.JPG

carli caps.jpg

Share this post


Link to post
Share on other sites

Kent, thank you so much for all of the info! 

I will try and take things apart today or tomorrow and send along some pictures of what I have going on. A quick clarifying question -

-When putting the sealant on the dust caps, I cover the entire cap including the edge/seal where it meets the speaker cone? In your picture it looks as though there's some sealant beyond that on the speaker cone itself too?

I also am recalling that the last time I took these speakers apart, several of the screw holes for the woofer were pretty stripped out. I remember doing the very crude trick of stuffing the holes with toothpicks to get the screws to grip, which worked, but I'm wondering if there's a better way. Would it be worth it to drill new holes, or is that too risky, and would also potentially create a poor seal for the woofer, unless I filled the old holes with something? 

Thanks for the links and suggestions on the duct seal, I will definitely be picking some of that up as if I remember there wasn't much of that left on the speakers. 

Thanks again, will get back soon with some pictures! All the best,

-Jared

 

Share this post


Link to post
Share on other sites

Hi Jared

The woofer in the picture had not been re-sealed so I guess the factory went a little over. You only need to seal the cap itself--not the woofer cone so no overlap there.

Stripped screw holes are common and your solution is fine. Maybe add a dab of wood glue to the toothpicks. OR, drill new holes. Be sure to fill in the old holes. I like the epoxy sticks available in hardware stores--you slice off a bit, knead it in your hand and press it in place. https://www.amazon.com/J-B-Weld-8257-KwikWood-Stick-1/dp/B002NJDAJY/ref=sr_1_4?ie=UTF8&qid=1547130354&sr=8-4&keywords=epoxy+stick

The duct seal is inexpensive and works well. If you're of my generation you may remember playing with plasticene "clay" and rolling it into snakes. Use the same method with the duct seal. just about 1/4" diameter should work.

If you go into the speakers, you may want to wear gloves and a mask when pulling out the fiberglass stuffing. Be sure to save the cloth that goes behind the woofer and re-use it when it all goes back together. It keeps fiberglass dust out of the woofer.

-Kent

Share this post


Link to post
Share on other sites

I finally got some time to begin restoring the 20's! 

Here's what I've done so far on one speaker:

-Removed and scraped off as much of the old Mortite as I could from where the woofer sits. 

-Removed everything from the cabinet (tweeter, insulation, crossover) and used Timber-Grip wood glue and ran a bead along all of the interior edges of the cabinet. I then used a toothpick to work as much glue as I could into the seams. I didn't have a clamp, but I read about someone using a couple ratchet straps so I gave that a shot and it seemed to have worked pretty well. I might do another bead of glue just to be safe or something like liquid nails, and also do the exterior rear panel seams as well, what do you think?

-The crossover doesn't appear to be quite what everyone else has going on. I don't know a ton about capacitors, but my crossover (that was recapped by the previous owner) has one 2UF-50V mylitic on the main plate and then a cap going to the tweeter that says "+8MFD-50V+" Is this correct? The speakers work fine and sound great (but maybe could sound even better?), any need to make a change here? How much do caps play a role in how these things sound? I read somewhere that someone complained that the Dayton caps made their 17s too bright sounding. I guess I want them to sound as close to original as possible. 

-The yellow foam gasket around the tweeter is completely flattened and falling apart, so I will probably use duct seal per your suggestion when reseating it, along with the woofer, or perhaps the craft foam for the tweeter and duct seal for the woofer. 

-The nails/staples on the crossover plate are pretty much non-existent at this point. The crossover was held in with two screws and some masking tape haha, and this was a major source of air leakage before I took the speaker apart. What would you recommend to reseat and seal this plate back on? Perhaps some kind of epoxy? I'm ok with it being permanent as long as it's airtight. 

-I'd like to shine up the walnut veneer on the exterior, and I've heard Howard Restore-A-Finish works really well applied with 0000 steel wool. 

-My cloth grilles are in ok shape but one of them is a bit ripped where my old cat got to them. The cloth also feels pretty stiff and I wonder if that's from age or if that's how they always were, and how much that might affect the performance of the speaker. There is definitely some resistance when I blow air from one side to the other. Has anyone ever put new fabric on these and what would you suggest?

Alright, that's all for now!(I tried attaching pictures, but they all say Upload Failed - is there a filesize limit? They're all around 800 kb.) Thanks all, -Jared

Share this post


Link to post
Share on other sites

Jared

I’m on the road without access to my files so maybe some other members will help 

You should have TWO 2uF caps and an 8uF. Check the schematic 

You could use the duct seal and some screws on the plate 

Michaels sells Charles Craft Irish linen which is good for the grilles and cheap with a coupon 

Resize your pics to about 100kb

Share this post


Link to post
Share on other sites

Thanks Kent, appreciate you taking the time to respond while you're on the road. 

I had a feeling the caps were off, I think while I have this all apart I might as well just recap. What types of caps last the longest? I'm willing to spend more for the best quality. Do the Daytons indeed sound "brighter?" 

Good call on the plate, that sounds like it'll do the trick, and thanks for the suggestion on the linen. In terms of taking off the old cloth and the 100 staples on it, would it be a better idea to cut the old cloth off around the backside, just leaving the back strip of old cloth and staples in place, and then putting the new cloth over that?

I've also treated the woofer surround with the vintage AR sealant, looks like 1 coat will probably do the trick, but I'll do the pressure test on the woofer once everything is back in place and see how the travel time is, and if it's too quick I'll try another very light coat after checking for other leaks. Will try and resize the pics later to post. Thanks! -Jared 

Share this post


Link to post
Share on other sites

I'm going to go with the Daytons for the recap, only thing is, Parts Express has the 2uF Daytons, but only has 8.2uF Daytons, not 8.0 (in fact I didn't see any 8.0 polys on there), will this make a difference? Thanks!

Edit: Did some googling and looks like that should still be in spec with the original? However, is the 250V on these ok?

Share this post


Link to post
Share on other sites

8.2 is fine 

Higher voltage is always good so yes— 250 is ok 👍 

Share this post


Link to post
Share on other sites
13 minutes ago, JKent said:

8.2 is fine 

Agree with Kent - - 8.2 will work - - but if desired and for a few more pennies, two Dayton 250V 4.0uF caps in parallel will get you there, too. 

Share this post


Link to post
Share on other sites

JayRd7 

I would recommend removing the staples in the old fabric. You'll need the room and it may affect the "thickness"" of the grill when you go over the top of all those staples and fabric. Be careful with the underlying black fabric, you'll want to reuse it. It may be very fragile, I have torn some in the past along the edges.   I've done several pair of Seventeens and Sixes with JKent' suggested  Charles Craft Irish Linen from Michaels and it is a very nice fabric and very inexpensive. I ended up using a hot glue gun because I could not find any staples short enough to not go through the Masonite and out the other end!

Photos are some Seventeens I just finished.

00x0x_jBySC0mAlWd_1200x900fabric3.jpg

fabric.jpg

Share this post


Link to post
Share on other sites

Thanks everyone for chiming in!

I bought the 8.2 caps, can't see the extra bit causing any real noticeable difference in sound (I hope right?), and regardless, I've never even enjoyed these speakers to their full potential since I've owned them as none of this work was ever done, so I know I'm in for a treat no matter what. From an audio perspective I'm curious, what would the extra 0.2 do in terms of the crossover, does it allow more HF to pass through to the tweeter, or restrict it, or something else entirely?

Thanks for the suggestion on the grilles, I will try to be delicate and hopefully won't destroy the Masonite trying to get all of the staples out. I may end up gluing as well based on what you said, unless I can find some short staples. Those Seventeens look fantastic! It's funny that the 20s didn't have a badge, but I noticed in the Masonite on mine there appears to be a pre-fab'd hole where one might go, as I'm sure they used the same grille boards for both these models. 

I have one cabinet pretty far along now, just need to wait on the crossover caps, but I used the Howard Restore-a-Finish followed by the Feed-n-Wax on it last night, and wow I couldn't believe what I had been missing out on all these years.It looks practically brand new. I have some chips in the wood here and there but that'll be an advanced project for me for a different time. 

And, finally got some pictures! Cabinets with and without the finish, woofer before surround treatment, gaps in the cabinet box that I ended up wood gluing and applying a thick bead of liquid nails to, the worn out tweeter foam, scraped off old Mortite from the woofer, and the incorrect crossover!  

 

    

IMG_5463.jpg

IMG_5453.jpg

IMG_5452.jpg

IMG_5451.jpg

IMG_5450.jpg

IMG_5449.jpg

IMG_5448.jpg

Share this post


Link to post
Share on other sites

That 2uF is a double cap. Replace it with two 2uF caps

I don’t bother replacing the black scrim cloth

You will never hear the difference between 8.0 and 8.2uF

Share this post


Link to post
Share on other sites

Awesome, thanks for the info! I got the second cabinet as far along as the first one now. Grille cloths are done and came out beautifully with that Irish linen. Now waiting on the caps to come in today so I can redo the crossover, then I should be ready to re-pack everything and seal the woofer with the duct seal. So I should roll little snakes and place them around the inner and outer rings of where the woofer sits? How thick in diameter? Or should I just cover every part of it and mold it into place with my hands?  I used craft foam and cut out a ring for the tweeter that fits nicely. I'll post some final pictures when it's all said and done!  Thanks again, -Jared

Share this post


Link to post
Share on other sites

Not sure what you mean by inner and outer

Just run a 1/4” or smaller diameter snake between the rim of the woofer and the cabinet where the Mortite was 

Share this post


Link to post
Share on other sites

The two rings that I marked red in this photo had Mortite on them (this particular picture doesn't show any Mortite residue on the inner ring but elsewhere there was a lot) so I wasn't sure if I needed to do both or just the outer ring. 

If all goes well I should have this done tonight! Pictures to come! Thanks, -Jared

 

 

IMG_5450.thumb.jpg.c38eb95d1bc3e7cc77d477354f982454.jpg

Share this post


Link to post
Share on other sites

Outer should do 

you just want to prevent air leaks 

Share this post


Link to post
Share on other sites

A labor of love, but oh so worth it! They sound and look incredible! I thought they sounded amazing before, but wow I'm pretty blown away. These really are magical speakers, there's something so lifelike and real about them, but at the same time with a musical character and warmth. They seem to be airtight now, especially the crossover plate which was the biggest offender before the restore - there is a bit of a delay now on the woofer return after pressing in, whereas before it was pretty much instantaneous, but I wonder if there should be more. The AR sealant guide said KLH's might need two coats, but I didn't want to overdo it. Maybe I'll post a video of it to get a better idea from you all. The bass response is definitely improved though, nice deep, tight and defined low end now, whereas before it was more boxy and smeared sounding.

A huge thanks to Kent and the others who gave advice guiding me through my first restoration. I've got the bug now, I think my next goal is to hunt down some 5's in need of some TLC! 

 

50439801_10218054503410231_6859764444814114816_o.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×