KLH Tweeter ID and Repair

[boreas]

Got a pic of a 6 and a 33.

Okay, I've got a job for you. Pull a tweeter from each and find out whether they have the same thickness top plate. That way we'll know where to place the Thirty-Three, with the Six, etc or with the Five, etc. (I've always heard the Six.)

John

 

[GD70]

Okay, I've got a job for you. Pull a tweeter from each and find out whether they have the same thickness top plate. That way we'll know where to place the Thirty-Three, with the Six, etc or with the Five, etc. (I've always heard the Six.)

John

My 6's do.

 

[audiojones]

Model Twelve, Five and Twenty-Three tweeters are interchangeable as you first posted.

The easiest (and pretty much the only) way to distinguish the Five/Twelve/Twenty-Three tweeter from the others is by the color of the adhesive used to hold the screen in place. The Five/Twelve/Twenty-Three uses a dark brown adhesive whereas the Six/Seventeen/Twenty uses a tan colored adhesive. *EDIT* - The backing plate thickness that is mentioned in the KLH service bulletin that doctorolds linked to on CSP is the most definitive way to tell the two drivers apart. Clearer pictures are in post #31 on page 3 of this thread. *END EDIT* You will often find M-12 stamped on the Five/Twelve/Twenty-Three tweeters as well, but not always.

The repair to the voice coil wire is pretty easy to do, I've done a bunch of them and that's usually all that is wrong with them. Heat up a knife or a flat blade screwdriver with a soldering torch and run it around the screen to pop it loose from the adhesive. Attach a very small gauge wire between the broken ends of the voice coil wire and solder it in place. Next use a hot glue gun and bury the wire in a small strip of hot glue (make sure that it doesn't touch the chassis of the tweeter assembly). Run a bead of hot glue around the edge of the basket and press the screen back into place after you have tested the tweeter and you are done.

Seems to be a very common failure, usually caused by corrosion at the soldering points (too much flux at the factory maybe?).

 

[BloFish]

How do you like the sound of the 6?

 

[GD70]

Model Twelve, Five and Twenty-Three tweeters are interchangeable as you first posted.

The easiest (and pretty much the only) way to distinguish the Five/Twelve/Twenty-Three tweeter from the others is by the color of the adhesive used to hold the screen in place. The Five/Twelve/Twenty-Three uses a dark brown adhesive whereas the Six/Seventeen/Twenty uses a tan colored adhesive. You will often find M-12 stamped on the Five/Twelve/Twenty-Three tweeters as well, but not always.

The repair to the voice coil wire is pretty easy to do, I've done a bunch of them and that's usually all that is wrong with them. Heat up a knife or a flat blade screwdriver with a soldering torch and run it around the screen to pop it loose from the adhesive. Attach a very small gauge wire between the broken ends of the voice coil wire and solder it in place. Next use a hot glue gun and bury the wire in a small strip of hot glue (make sure that it doesn't touch the chassis of the tweeter assembly). Run a bead of hot glue around the edge of the basket and press the screen back into place after you have tested the tweeter and you are done.

Seems to be a very common failure, usually caused by corrosion at the soldering points (too much flux at the factory maybe?).

I just attempted this on one of mine and the only way I would get any kind of ohm reading was when I pressed the new wire down onto the brown cone support. When just holding the new wire to both ends of the broken wire, again this was the when I could get a reading, not when just the wire ends were touching. I'm a bit stumped. Also the wire is from some very fine twisted steel cable which I pulled off one strand. Should I be using copper wire instead?

 

[audiojones]

I just attempted this on one of mine and the only way I would get any kind of ohm reading was when I pressed the new wire down onto the brown cone support. When just holding the new wire to both ends of the broken wire, again this was the when I could get a reading, not when just the wire ends were touching. I'm a bit stumped. Also the wire is from some very fine twisted steel cable which I pulled off one strand. Should I be using copper wire instead?

Yes, definitely use copper wire. I usually pull some stands of fine copper wire to do this repair or else I'll use the braided copper voice coil connection wire from a junk speaker (that braided wire that goes from the terminal strip to the cone connection).

If the break in the voice coil wire is below the cone then you're out of luck on that tweeter. If you can get an ohm reading at a point above the cone then that's where you make your connection with the new wire. If you only get an ohm reading when you push in on the cone then you're out of luck, that means the break in the wire is below the cone.

Hope this helps!

 

[GD70]

Yes, definitely use copper wire. I usually pull some stands of fine copper wire to do this repair or else I'll use the braided copper voice coil connection wire from a junk speaker (that braided wire that goes from the terminal strip to the cone connection).

If the break in the voice coil wire is below the cone then you're out of luck on that tweeter. If you can get an ohm reading at a point above the cone then that's where you make your connection with the new wire. If you only get an ohm reading when you push in on the cone then you're out of luck, that means the break in the wire is below the cone.

Hope this helps!

Thanks Audio.
I didn't press the actual paper cone. The new piece of wire when touching both ends of the broken wire did not give me a reading unless it was pressed firmly on the cone surround, the hard brown ring around the cone.

I'll try some copper wire from a junk speaker and see if this makes a difference. Why do they use such thin wire here to begin with?

 

[boreas]

The easiest (and pretty much the only) way to distinguish the Five/Twelve/Twenty-Three tweeter from the others is by the color of the adhesive used to hold the screen in place. The Five/Twelve/Twenty-Three uses a dark brown adhesive whereas the Six/Seventeen/Twenty uses a tan colored adhesive.

I've seen the different color adhesives but never associated it with the two different tweeter types so I never bothered to check my Twenty-Threes until just now. The adhesive on them is sort of a warm honey brown. I guess that's what you're referring to.

What are your thoughts about the service bulletin the OP posted which indicates that the top plate of the magnet assembly is different (thinner) on the M-12 type tweeter than on the other? So far, that's proven consistent in the tweeters inspected in that context here. It strikes me that a difference of that significance would be more definitive than the color of the adhesive used.

John

 

[audiojones]

I've never checked out the backplate thickness theory, I'll have to look into that one. I remember reading it on CSP years ago but I guess it didn't register with me since I could see the different adhesive color on front. I have never once seen a Model Five, Twenty-Three or Twelve that didn't use dark brown adhesive on the tweeter and likewise I've never seen one of the other models with anything but tan adhesive. Even the black painted tweeters have tan adhesive when the black paint is scrapped off.

I read in an interview with Henry somewhere (maybe its posted on CSP somewhere?) that the two tweeters were identical except for some cone dampening changes and a few other "tweaks" done at the factory but he was very ambiguous about exactly what thy were.

I spent some time comparing them side by side and the Five/Twelve/Twenty-Three tweeter sounds a bit more defined and delicate in the highs whereas the Six/Seventeen/Twenty tweeter has more of a midrange hump tending towards a slightly over exaggerated presence (kind of "squawky" in comparison) and the highs are slightly less articulate. Quite frankly I doubt anyone would really object to a pair of the other tweeters being substituted in for the originals, but the properly damped and "tweaked" tweeters are the correct ones for the crossover point and they sound better to me.

 

[doctorolds]

I would first like to thank you all for your input so far. It appears as if we creating a method in which to better or more properly identify the KLH tweeters. It also appears as if the two groups of tweeters and their usage has been stated on this forum and others has been fairly accurate, at least as far as I can tell. As of now the top plate used on the magnet and the color of adhesive used appear to be the two factors used to identify a KLH tweeter.

I removed the tweeters from my Model 5's today and they have the thin top plate also. Maybe someone can provide a picture of the two types of tweeters from the front so we can see the difference in the color of the adhesive used as "audiojones" has stated. I cannot imagine how many KLH tweeters have been thrown away without trying to repair them, what a shame.

Any further input by AK members will be greatly appreciated, and may provide the answer(s) to properly identifying the two types of KLH tweeters. I am wondering if the anodized version has a thin or thick top plate also.

I hooked mine up to my Sansui 9090 today and was pleasantly surprised. I cannot wait to restore them and hear them as designed to be heard. I attached a couple of photos for you all. Thanks again!

 

[audiojones]

I was just digging around in my parts box in the attic to find two examples to compare. Naturally the only Six/Seventeen tweeters I have are black so you can't compare the adhesive colors. *EDIT*- On closer inspection I now see that you are talking about the lower plate on the magnet and you are 100% correct - it is THICKER on the Model Six, Seventeen, Twenty tweeter and THINNER on the Model Five, Twelve and Twenty-Three tweeter. It's very obvious now that you have pointed it out, I will take a closer photo and post it below.

I tried scraping a little of the black paint off and you can kind of see the glue underneath - it's an off white or light tan glue as opposed to the darker glue used on the Twenty-Three tweeter on the left. It's not as easy to see here but with a silver one it's very distinguishable. A silver one with off-white glue or a black one is for the Six, Seventeen, Twenty etc. However it looks like the backing plate thickness is the best way to tell.

BELOW: The Model Five/Twelve/Twenty-Three tweeter is on the left with the THINNER magnet back plate and the Model Six/Seventeen/Twenty tweeter is on the right with the THICKER magnet back plate. The plate above the magnet is the same on both styles, it's the plate between the back of the speaker and the bottom of the magnet that is different.

 

[boreas]

*EDIT*- On closer inspection I now see that you are talking about the lower plate on the magnet and you are 100% correct - it is THICKER on the Model Six, Seventeen, Twenty tweeter and THINNER on the Model Five, Twelve and Twenty-Three tweeter. It's very obvious now that you have pointed it out, I will take a closer photo and post it below.

Yeah, the wording in the Service Bulletin confused me too. At first I thought they were talking about the flange.

So, it would seem that there are two ways to distinguish one type from the other, the color of the adhesive and the thickness of the top plate in the magnet assembly.

John

 

[audiojones]

Yeah, the wording in the Service Bulletin confused me too. At first I thought they were talking about the flange.

So, it would seem that there are two ways to distinguish one type from the other, the color of the adhesive and the thickness of the top plate in the magnet assembly.

John

Yeah but the magnet backing plate seems like a very solid structural difference that can't be mistaken if one knows to look for it. Hopefully the picture above will help folks distinguish between the two in the future. Hey, I learned something today - thanks!

 

[boreas]

Yeah but the magnet backing plate seems like a very solid structural difference that can't be mistaken if one knows to look for it. Hopefully the picture above will help folks distinguish between the two in the future. Hey, I learned something today - thanks!

Thank the OP! He found that service bulletin on CSP.

John

 

[audiojones]

Thank the OP! He found that service bulletin on CSP.

John

Thanks doctorolds! I read that service bulletin on Classic Speaker Pages a long time ago but it never made sense until you and John deciphered it. Glad you brought it up :thmbsp:

 

[doctorolds]

My pleasure, and thank you, "audiojones" and "boreas" for your useful comments and verification of the top plate being one way besides the color of the adhesive to identify a KLH tweeter.

I am still wondering about what page 2 of the SB has on it an addition to further identifying of the anodized KLH tweeters. Maybe someone will provide some more input.

 

[doctorolds]

Here are a few more pictures that may allow someone to see the differences in the two types of tweeters more clearly.

Photo 1 and Photo 2 show the difference in the color of the adhesive and Photo 3 shows the difference in the thickness of the magnets top plate.
*EDIT* The all black tweeter on the left is for Models 6, 17, 20, 30, and 33.
*EDIT* The all silver tweeter on the right is for Models 5, 12, and 23.

I will provide a couple of pictures of the repair of the tweeters once completed.

 

[boreas]

Here are a few more pictures that may allow someone to see the differences in the two types of tweeters more clearly.

Photo 1 and Photo 2 show the difference in the color of the adhesive and Photo 3 shows the difference in the thickness of the magnets top plate.

I will provide a couple of pictures of the repair of the tweeters once completed.

Great! The more data we have on I.D. and repair the better.

Thanks!
John

 

[chrisand4]

Just an update, I got my caps in today. I recapped my model 33, and I can confirm the tweeter top-plate is identical to the one on my 6. The glue color is the same too; to me they look like the same tweet.

The 33s sound wonderful by the way, and I can't wait to find another tweeter so I can compare them to the 6.

 

[Soundminded]

The tweeter was originally developed for the Model 6. It first appeared in 1958. It was the result of trial and error for hundreds of different designs. The manufacture of Model 6 alone lasted until 1972 so there were many variants in the details of manufacture but they should perform all the same. In fact KLH guaranteed that each speaker would perform within +/- 1db of the prototype over its entire range long before there was an ISO9000 process. Along with AR product that passed inspection for shipment from the factory were among the most consistent in performance and quality. Model 17 was developed as a lower cost alternative to Model 6. 6 went head to head against AR2 series, 17 was intended to target AR4 series. Model 5 added the two midrange speakers that were actually also used as full range drivers in their table radios like Model 8 and some of their small all in one systems. It was inteded to compete with AR3 sereis and may have had a better woofer but the same size as model 6. Model 12 was also 3 way in a lowboy enclosure with a four switch crossover each with 3 positions (there were no graphic equalizers available to consumers in those days.) AFAIK, all have interchangeable tweeters. I'm not sure about the others but they are also probably the same.