KLH Model Twelve project log

[carydf]

Hi All,

I was given a pair of KLH Model Twelves. I hope to rebuild them.

My first question has to do with the woofer. The existing speakers have decayed foam surrounds. They are not original. Whomever did the re-edge did a nice job but it was a long time ago. I'd like to replace them with cloth surrounds instead of foam.

What kind of cloth is best for the surrounds? I found lots on info on glue and tons of discussion on coating the cloth with any number of alternatives but not one thing about what type of cloth to use for the surrounds.

Thanks,

Carydf

[dynaco_dan]

Hi All,

I was given a pair of KLH Model Twelves. I hope to rebuild them.

My first question has to do with the woofer. The existing speakers have decayed foam surrounds. They are not original. Whomever did the re-edge did a nice job but it was a long time ago. I'd like to replace them with cloth surrounds instead of foam.

What kind of cloth is best for the surrounds? I found lots on info on glue and tons of discussion on coating the cloth with any number of alternatives but not one thing about what type of cloth to use for the surrounds.

Thanks,

Carydf

Hi there

The OEM woofers that were used in the KLH Twelves and all classic KLH woofers was a treated cloth, not foam, luckily.

There has been a few mentions on the net about gauze with a treatment but nothing otherwise.

I've not read anything about the original cloth type surrounds being available, yet.

Do you have the separate contour control boxes?

If so, they can be updated, if necessary, with larger wattage rated resistors and PP capacitors.

Quite a bit has been written here about that, especially by, Kent.

Photos please.

[carydf]

I have the control boxes. Both are in good condition. I have not opened them up to see what they look like on the inside.

I pulled one of the woofers and tested them to with a VO meter. One is open. Since its beginning to get more complicated that just re-edging I tested the control boxes and the mids/tweeters (without pulling them from the cabinets). One speaker is good and the other .... not so good.

I will pull the mids and tweeters to test them on the bench next free moment. Pictures will be forth coming.

[dynaco_dan]

I have the control boxes. Both are in good condition. I have not opened them up to see what they look like on the inside.

I pulled one of the woofers and tested them to with a VO meter. One is open. Since its beginning to get more complicated that just re-edging I tested the control boxes and the mids/tweeters (without pulling them from the cabinets). One speaker is good and the other .... not so good.

I will pull the mids and tweeters to test them on the bench next free moment. Pictures will be forth coming.

Hi there

Your contour controller may be defective.

There is many photos, mostly by Kent, of the KLH control box resistors, burnt.

If burnt, they may be open.

The red/black caps are bad usually and maybe also open.

Remember that if you want to test an individual driver, disconnect it from the crossover and use a 1 1/2 volt battery, no larger.

[carydf]

One of the control boxes works. Probably still have to be rebuilt but it works enough to tell me if the tweeters and mids are working. Thats how I know the tweeters and mids on one speaker is working but not the other.

[JKent]

Hi Cary and welcome

I'm away from home and can't offer much advice right now, but:

The woofers should be the same as the KLH Five.  Just be careful if shopping on ebay. KLH called these "12 inch" woofers but, as has been discussed here, they actually measure about 10.75" (IIRC). So they are sometimes advertised on the bay as 10" or 11". Be sure, if you buy replacements, that they were pulled from a KLH 5 or 12. EDIT: This is years after the fact but experience has shown that the Five and Twelve woofers are NOT the same. The Twelves have double magnets. I've added photos to show the difference between the Five (single magnet) and Twelve. Sorry for this misleading post. -K

The mids are easy to come by. Called the "12.5" (no idea why) they were used in KLH radios and in several speakers, including the 5, 12, 14, 15, 19 and others.

Not sure about the tweeters. They are the same in the 5 & 12, & others but don't recall which.

There is a thread here on recapping the crossover. I strongly recommend replacing the resistors as well, as Vern noted, because the originals are 5 watt and I have seen burned and cracked resistors in the 5 and the 12.

Good luck. I'll check in again in 3 days. The KLH Twelves are truly great, often overlooked speakers IMHO. Get them working properly, with new caps & resistors, re-dope the surrounds as described in the service bulletin #61 (in our Library) and they will rival the revered AR3a (IMHO).

Kent

[dynaco_dan]

Hi Cary and welcome

The woofers should be the same as the KLH Five. Just be careful if shopping on ebay. KLH called these "12 inch" woofers but, as has been discussed here, they actually measure about 10.75" (IIRC). So they are sometimes advertised on the bay as 10" or 11". Be sure, if you buy replacements, that they were pulled from a KLH 5 or 12.

The mids are easy to come by. Called the "12.5" (no idea why) they were used in KLH radios and in several speakers, including the 5, 12, 14, 15, 19 and others.

Not sure about the tweeters. They are the same in the 5 & 12, & others but don't recall which.

There is a thread here on recapping the crossover. I strongly recommend replacing the resistors as well, as Vern noted, because the originals are 5 watt and I have seen burned and cracked resistors in the 5 and the 12.

Good luck. I'll check in again in 3 days. The KLH Twelves are truly great, often overlooked speakers IMHO. Get them working properly, with new caps & resistors, re-dope the surrounds as described in the service bulletin #61 (in our Library) and they will rival the revered AR3a (IMHO).

Kent

Hi there

Just to add to Kent's comment about the KLH Five and KLH Twelve woofers.

I believe it was klhmark that had worked previously at KLH, he posted the two driver sheets that are in the library.

There was more than one model of woofer used, or variant at least, not identified on the sheets.

The cone weight and magnet configuration is about the only physical trait they have.

I will find and post some of the variations that I have photos of, soon.

The main difference is the cone weight but more importantly, the depth of the magnet.

There was a bump stamped in the back plate at some point in time, to allow a greater excursion of the woofer, on deep bass.

I do not know what effect that had other than allowing a longer excursion distance before bottoming, which is real bad.

There was several variants of the normal magnet as well.

The cones were felt marked, on the front or back of the cone material, with perhaps 23 - 25.

This is the weight of the cone material and it reserved it for use only with the KLH Twenty-Three, Five and Twelve speaker systems.

Other lower weighted cones were used in other lesser speaker systems.

I do not know what using a lighter weighted cone would do or in reverse using the heavier cone in a lower speaker system.

Even after seeing what a seller is offering, just post a question here if you are uncertain.

Buying from someone not conversant in KLH products, may offer the right physical drop in sized woofer, but wrong model number.

There is usually no identifying marks, such as model number to easily say which is the correct and final production unit.

I believe that there is sometimes a rubber stamped date on the magnet, which may or may not be readable even.

Just because a seller says it is the correct woofer is not always the correct answer.

I've seen sellers offering drivers for several brands, one example Dynaco, which is 8 ohms and the seller is selling 4 ohm drivers ( used in B&O speakers ).

The cone with a felt marked 5 as well, was very likely removed from a KLH Five speaker system.

There is other woofer magnets that I have not photographed yet, at least you can see the different cone weights here as well.

Some of my photos are off the internet.

[carydf]

Thanks for the info. I have to put the project on hold for now due to work issues. I will check back in once in a while as time allows to update progress ... but its going to be slow for a while.