Model Twelve Crossover

[meta_noia_fot]

I bought a pair of Model Twelves that need a restoration. I’ve ordered replacement caps and resistors but I have a question about the double 4mfd since there’s no available schematic. 
 

If I twist a pair of new 4mfd caps together so that they share a common lead, would that be the black wire in this photo of the crossover? That would leave the far ends of the double cap to take the place of the red wires. 

Thanks in advance 

 

[JKent]

That's right. Is that your only double cap? Sometimes KLH used a double cap but both red leads went to the same point, so a single cap can be used instead.

Kent

[meta_noia_fot]

@JKent Thanks for your help! Those diagrams are terrific. 
 

And yes, that is the only double cap on mine. Speaking of, here’s a couple photos. Oddly enough, mine had two 47mfd caps instead of the two 50mfd. Pic of those too. They didn’t strike me as original but they were fastened down with the original cable tie. Maybe someone replaced the 50s and shoved the 47s under the same tie. I ordered 50mfd as replacements based off your previous work on the Twelve. Hopefully when I’m done my crossovers will look half as clean as yours.  

[JKent]

Yeah, those 47s are definitely new. And 47 is close enough to 50. You'll notice in my re-do, some caps and some resistors are close but not exact values.

Speaking of which, it may be too late now but I always recommended replacing all of the 5w resistors with 10w. RoyC looked into this and identified just 1 or 2 that had to be replaced. I have to search my notes. One is the 5 ohm in the upper left corner in my pic. I'll try to get more info.

Kent

PS: OK. I think Roy said that 5 Ohm resistor in the woofer circuit should be 15 0r even 20 watts. There's a 15 Ohm in the mid circuit. I think it's the one in the middle of the board. That one's OK but could be bumped up to 10w. The other 5w resistors are fine.

PPS: OOOPS. We were typing at the same time.

[meta_noia_fot]

Thanks Kent. I already have replacement resistors coming in with the caps. I followed that same advice on my Fives as well. I ordered 15w resistors just because it was convenient for values from the supplier I used. 

[meta_noia_fot]

21 minutes ago, JKent said:

PS: OK. I think Roy said that 5 Ohm resistor in the woofer circuit should be 15 0r even 20 watts. There's a 15 Ohm in the mid circuit. I think it's the one in the middle of the board. That one's OK but could be bumped up to 10w. The other 5w resistors are fine.

PPS: OOOPS. We were typing at the same time.

You and Roy are a wealth of knowledge on these. Thanks. 
 

I originally started this thread for questions about the crossovers, but I guess I’ll add some questions and observations about the cabinets. 
 

While I wait for caps and resistors, I’ve been working on resealing the cloth surrounds and sealing the drivers into the cabinets. 
 

Currently I have OK seals on the woofers. That’s after one layer of Roy’s sealant on the woofer dust cap and 2.5 layers on the surrounds (2 full coats and a touch up of spots that looked thin). When pushing in and releasing the woofer, I get a second or so before the woofer is back in its original position. Judging it against the seal on my Fives, it’s not quite as good…the woofer maybe returns in half the time as on the Fives. Is there anything about the large volume cabinet on the Twelves that complicates this process or should I be getting a similar seal here? It’s possible I still have some leaks I haven’t found. 
 

As for the midrange drivers, what’s the best way to tell they are sealed? On the Fives I just push one cone in and see if the other pushes out since they share the same enclosure. But since these have separate enclosures on the Twelve, is there a way to tell how sealed these are? I resealed each surround and plugged up the drilled wire holes inside each cabinet. A push-and-return test is pretty inconclusive to me on the midranges. Maybe they’re fine as is and I’m overthinking it. 
 

Speaking of the midrange enclosures, those are held on with four screws on the front of the baffle, unfortunately right where each midrange needs to seal. So more than not, each of those screw holes ended up with a small channel into the enclosure. I used duct sealer to plug those holes and to reseal the drivers. It’s unsightly but at least the grills and original grill cloth are intact so no one will have to see it. 
 

George

[RoyC]

5 hours ago, meta_noia_fot said:

Currently I have OK seals on the woofers. That’s after one layer of Roy’s sealant on the woofer dust cap and 2.5 layers on the surrounds (2 full coats and a touch up of spots that looked thin). When pushing in and releasing the woofer, I get a second or so before the woofer is back in its original position.

As for the midrange drivers, what’s the best way to tell they are sealed?  Maybe they’re fine as is and I’m overthinking it. 

Speaking of the midrange enclosures, those are held on with four screws on the front of the baffle, unfortunately right where each midrange needs to seal. So more than not, each of those screw holes ended up with a small channel into the enclosure.
 

George

Hi George,

Based on your post, I'm sure you have plenty of sealant on the woofer and mid surrounds. As long as your woofer cones are returning more slowly. There is such a thing as applying too much sealant.

The mids' surrounds only need one light application of sealant, which is much less necessary than the supplemental treatment of the woofer surrounds. It is more important to keep the mids' surrounds compliant. The most critical aspect of installing the mids is sealing their sub-enclosure from the rest of the cabinet.

The mids originally had white foam gaskets in the space you filled with putty. There should be some kind of gasket material under the entire mounting flanges of all the drivers.

Roy

PS Great photos, Kent.

[meta_noia_fot]

Thanks @RoyC. I had read previously that less sealant was needed on the mid surrounds. Those received a very light application. I also tried to be judicious with my use on the woofer surrounds, some areas still were not tacky or shiny after the second coat (primarily edges where the surround meets the cone and basket).

I replaced the white foam gasket material with a ring of duct seal. I figured it may be better being able to press it into those screw channels. The above photos were before I installed the rest of the duct seal and screwed things down. I do think the seal is better now than with the old compressed white gasket.

Thanks for your help

George

[RoyC]

Any time. Sounds like you have everything under control. Keep us posted.

[meta_noia_fot]

I had to replace one of the crossover boxes with one from eBay. When I opened the original up, there was a healthy mold specimen in the wood. 
 

I received the replacement crossover in the mail and it looks closer the original one that Kent posted. Thought it would be interesting to show them side by side, bearing in mind that the 50mfd caps in the crossover on the right were already replaced as mentioned above. 

[meta_noia_fot]

I finished replacing all the caps and resistors. I’m going to go back and hide solder connections with electrical tape, but they’re finished enough that I’m able to test them. I haven’t done work this extensive on many crossovers; feedback appreciated.

Lovely sound, as expected. Tomorrow I’ll a/b them against the Fives. 

[DavidR]

Nice, neat work.

 

[meta_noia_fot]

Thanks @DavidR. It’s nice to have external crossover boxes (or easily-removable crossover boards like the Model Five). Much easier to make work look neat when you’re not working inside a cabinet. I thought the Five and Twelve crossovers were both fun projects. 

[meta_noia_fot]

Well I’ve spent my listening time today split between the Model Five, Model Twelve, and AR-3a.

It’s not necessarily an even playing field; the -3a’s mids and tweeters have not been rebuilt, while I don’t believe the KLH drivers need any more restoration. 

But a couple of observations:

In terms of pure, low frequency response, I think the -3a has the edge. A/B’ing between the -3a and Twelve using modern electronic music and some organ music, the -3a handles very low tones better. But it’s close. 

Between the Five and the Twelve (all tone controls flat), the Five sounds more forward on the mids and highs. I like both the KLH models over the -3a for rock music. Another fun experience was playing the Fives and Twelves together. That’s an impressive rock setup. 

Here’s a pic of the stack at the moment. All three of these projects wouldn’t have been possible without this forum, so thanks as always for that. 

George

[JKent]

Forget about stacked Advents. Your stack rocks!

[meta_noia_fot]

I’m looking for some cabinet advice. 

Since these have external crossovers, I wanted to listen to these awhile before deciding to undertake any cabinet work. Now I’d like to know, what could be done about the cabinets? 

Pictures are of the worst of the two; the other doesn’t have water damage. The corner splits are cosmetic only and the interior of the cabinet is still sealed. Lots of miscellaneous scratches like the one pictured on the front. 

[meta_noia_fot]

Here’s a couple specific questions about the cabinets:

1. Would clamping the corner split in any way improve it or is it too far gone since the boards have swollen from moisture? Is there anything else that could be done?

2. Is there anything that can be done about the finish on the top and on scratches? Does the Twelve use the same, hard to remove finish that the Five does? Normally I might try Howard’s Restor-a-finish as a first attempt but not sure if that will work on these. 

The parts that are rough, are pretty rough. They’re not complete eyesores, but they’re not beautiful either.

I think these are very nice sounding speakers and deserving of better looking cabinets, just not sure of the feasibility of some of what needs to be done. This is something I’d tackle longer term—probably late summer. My confidence with crossover work is much higher than with cabinets. Any help would be greatly appreciated. 

[JKent]

Glenn is the expert on this, but I'll take a crack at it

1. Before clamping, dig out as much crumbly/swollen stuff as you can.
2. Sorry I don't remember what the finish is. I'd try wiping it with Lacquer thinner first. If that softens it, it's lacquer.  If there are dents, where the fibers aren't torn up, you can steam them out with a damp cloth and an iron (even a soldering iron).

Good luck. Worthy speakers.

Kent

[meta_noia_fot]

Thanks @JKent. 

6 hours ago, JKent said:

Sorry I don't remember what the finish is. I'd try wiping it with Lacquer thinner first. If that softens it, it's lacquer.  If there are dents, where the fibers aren't torn up, you can steam them out with a damp cloth and an iron (even a soldering iron).

I never would have thought about steaming dents. I’ll keep that in mind. 

I’m worried this has the same lacquer finish as the Five. Looking at the most damaged top again today, I can scratch off some of the most damaged finish with my fingernail. I’m also concerned some of the black spots will need to be bleached out of the wood. 

[JeffS]

I used the steam method to remove a couple of creases on an AR-3 and it worked very well.

The speaker has an oiled finish and and the steam process removed the oil, changing the color.

Just something to keep in mind. I'm not sure how lacquer would react to it.

[meta_noia_fot]

5 hours ago, JeffS said:

Just something to keep in mind. I'm not sure how lacquer would react to it.

Thanks. The lacquer on these cabinets is certainly going to complicate each step of this. 

[RoyC]

1 hour ago, meta_noia_fot said:

...The lacquer on these cabinets is certainly going to complicate each step of this. 

The finish appears to be similar to the AR-2 cabinets you are discussing in the AR section. It will be interesting to see what the wood guys recommend. There is no shortage of nasty old KLH cabinets out there.