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KLH tweeter burnout -- can it be caused by crossover problems?

F

FrankieKat

New Member
I was very happy to have scored a pair of KLH Model Fives, rescued from a neighbors' trash. They had all the typical problems... dried-up seal on woofers, original crossover caps and one bad tweeter. Using RoyC's magic re-sealant and all brand new caps I fixed two of the problems and put it all back together and did a test with the speaker with one of the good tweeters.

It played wonderfully for about 5 minutes, and then the tweeter cut out for about 2 seconds and came back. About 3 minutes of play later the tweeter went out again and didn't come back. I checked the connections and then checked the tweeter with an ohmmeter and it now measures near open (about 1.2Mohms). Bummer!

So before I take on an unhealthy KLH tweeter buying habit, I'm wondering if perhaps there's something else going on here that I should look into first. I checked all of the wire resistors and they tested fine, and all caps are now brand new. I re-capped the speaker with the burned out tweeter first, and put the good tweeter from other one into this one, so it's the same crossover and other drivers as the one with the tweeter found DOA.

Is it possible that perhaps something else in the crossover is failed and causing the tweeter to burn out? Perhaps this thing was just moments away from death due to whatever causes them to fail? Anyone ever seen these things fail right in front of your eyes?

FK :confused:
 
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Yep, I've seen them fail from time to time. Usually it's the little hair-thin wire under the mesh screen that leads into the cone. The flux they used when soldering the ends is corrosive and if they didn't clean it off very well it tends to eats through the end of the wire causing an intermittent and eventually open circuit in the tweeter.

I usually heat up a putty knife with a soldering torch and carefully run it around the glue seal holding the mesh screen in place. Once the screen is unglued you will probably see your issue - a very fine wire that solders to the terminal end that's hanging loose. I generally use one strand of fine wire, make a hook in the tweeter's wire and the new wire, hook 'em together and solder. Then solder the other end to the terminal end, test everything and if it's ok glue the screen back in place with hot glue.

I've done a bunch of them over the years, and with those KLH speakers if it isn't the caps it's usually the voice coil wire end. Caps should always be replaced anyway since they are very poor quality and prone to failure, so you're ahead of the game.
 
audiojones said:
Yep, I've seen them fail from time to time. Usually it's the little hair-thin wire under the mesh screen that leads into the cone. The flux they used when soldering the ends is corrosive and if they didn't clean it off very well it tends to eats through the end of the wire causing an intermittent and eventually open circuit in the tweeter.

I usually heat up a putty knife with a soldering torch and carefully run it around the glue seal holding the mesh screen in place. Once the screen is unglued you will probably see your issue - a very fine wire that solders to the terminal end that's hanging loose. I generally use one strand of fine wire, make a hook in the tweeter's wire and the new wire, hook 'em together and solder. Then solder the other end to the terminal end, test everything and if it's ok glue the screen back in place with hot glue.

I've done a bunch of them over the years, and with those KLH speakers if it isn't the caps it's usually the voice coil wire end. Caps should always be replaced anyway since they are very poor quality and prone to failure, so you're ahead of the game.
Click to expand...

Bingo! That was the problem on both of the tweeters... guess the one was just hanging on and a little bit of vibration from playing knocked it loose. On one of them both leads were actually broken and in all cases the break was right where the voice coil leads enter the potting material just at the edge of the cone. I was able to carefully re-attach new leads and both of them came back to life!

In my earlier research I found many threads where people reported open coils on these tweeters and the resolution was often to replace it. Unless the wire is broken right where it enters the voice coil I'd imagine that many could be fixed. I did find this post that discusses these repairs: http://www.audiokarma.org/forums/showthread.php?t=492609#post6390209

I haven't tried to re-attach the metal grill with the old sealant -- anyone have any success trying to reconstitute it, perhaps with some heat? Or just try to scrape it all off and use a different adhesive?

Thanks for the tips -- two more KLH tweeters saved!

FK
 
Sweet! I imagine many KLH tweeters have been needlessly trashed because of the wire end issue, unfortunately. I have never tried to reuse the old glue, I usually just clean it off as best as possible and then reattach the screen using a hot glue gun. I also put a dab of hot glue on the splice to protect it from corrosion and to prevent it from shorting against the metal screen.
 
audiojones said:
Sweet! I imagine many KLH tweeters have been needlessly trashed because of the wire end issue, unfortunately. I have never tried to reuse the old glue, I usually just clean it off as best as possible and then reattach the screen using a hot glue gun. I also put a dab of hot glue on the splice to protect it from corrosion and to prevent it from shorting against the metal screen.
Click to expand...

Timely thread. I was listening to my 5's a week or so back and mid-song the left speaker totally cut out. It had been completely recapped, etc. a year back and I now suspect it's the tweeter. I haven't had the energy to look into the problem.

What wire do you use to fix the tweeter? do you just create a link between the broken leads or do you just replace from one break all the way to the terminal?

When you say "I also put a dab of hot glue on the splice to protect it from corrosion and to prevent it from shorting against the metal screen.," do you mean that you hot-glue the newly fixed wire to the cone itself?
 
dodog said:
What wire do you use to fix the tweeter? do you just create a link between the broken leads or do you just replace from one break all the way to the terminal?

When you say "I also put a dab of hot glue on the splice to protect it from corrosion and to prevent it from shorting against the metal screen.," do you mean that you hot-glue the newly fixed wire to the cone itself?
Click to expand...

The wire usually breaks at the very end where it connects to the terminal (not always, but often). I create a link between the broken end of the wire and the terminal connection with a single strand of ordinary wire (speaker wire, lamp cord wire, whatever is available) that is roughly the same gauge as the broken lead-in wire. I put a dab of glue on the metal frame of the tweeter, lay the newly soldered splice into the dab and then put a small dab over it. That way it won't short out against the metal frame of the tweeter or the metal screen above. Next time I do one I'll take some photos and post it - they're pretty easy to fix and it's a common problem.

Sometimes the wire breaks where it enters the voice coil in the tweeter. When that happens it's toast AFAIC, although there may be some folks out there who will dig deeper and fix that problem too. Usually they break at the very ends though because the soldering flux wasn't cleaned off at the factory and it rots the wire out.
 
audiojones said:
Sweet! I imagine many KLH tweeters have been needlessly trashed because of the wire end issue, unfortunately. I have never tried to reuse the old glue, I usually just clean it off as best as possible and then reattach the screen using a hot glue gun. I also put a dab of hot glue on the splice to protect it from corrosion and to prevent it from shorting against the metal screen.
Click to expand...

I ended up using a heat gun on medium-low and was able to get the original glue to reflow and reform around the cover. It got a little bit darkened in a few places, but once it cooled down it seems to be as solid as before. So it is possible!

FK
 
I also have a pair of fives I am refinishing and just ordered the caps. My tweeters have been fine but I wonder if I could "repair" the corrosion before it breaks? I haven't opened the tweeter yet to peek in there but maybe a drop of solder could be added to this connection after a gentle cleaning? They are from 1969 so would like to do something before it totally breaks. Thanks for any replies.
 
Cool, good to know that the screen glue can be re-flowed! I've got a pair of Model Fives here that are missing the metal screen covers on the tweeters. I don't see any signs of repair on them so I guess the previous owner decided to take the screens off for sonic reasons? They do sound brighter than the usual KLH tweeter, I wonder if that's why. The previous owner recapped them with Daytons (did a nice job too) and all the values are correct.
 
audiojones said:
Yep, I've seen them fail from time to time. Usually it's the little hair-thin wire under the mesh screen that leads into the cone. The flux they used when soldering the ends is corrosive and if they didn't clean it off very well it tends to eats through the end of the wire causing an intermittent and eventually open circuit in the tweeter.

I usually heat up a putty knife with a soldering torch and carefully run it around the glue seal holding the mesh screen in place. Once the screen is unglued you will probably see your issue - a very fine wire that solders to the terminal end that's hanging loose. I generally use one strand of fine wire, make a hook in the tweeter's wire and the new wire, hook 'em together and solder. Then solder the other end to the terminal end, test everything and if it's ok glue the screen back in place with hot glue.

I've done a bunch of them over the years, and with those KLH speakers if it isn't the caps it's usually the voice coil wire end. Caps should always be replaced anyway since they are very poor quality and prone to failure, so you're ahead of the game.
Click to expand...

Okay I replaced my 23's tweeter (with a proper stock replacement) but never got rid of the original. Just want to make sure I am reading this correctly!

The wire in question is the on the front of the tweeter.

1) remove the screen and look at the fine wire going to the cone.
2) daisy chain broken wire with fine copper wire then solder

Does anyone have any pics to clarify if possible I would like to save the tweeter rather than let it collect dust.
 
Now, as paranoia sets in; looking back there has not been a lot of.Talk about the Fives until recently, around the time I found out my old set was headed back my way. First it was caps, then sealing everything tighter than a top secret document and now, tweeters. I'm not ever going to sleep soundly again.

As of today, at least, mine are both working. But, now I have to worry about tomorrow and I do not have the sealing done, yet.
 
Seal the surrounds, re-cap if not done, enjoy! If a tweeter cuts out, then fix or replace. Not worth loosing sleep over.

Glenn
 
My hearing is not so good but I can say for sure that my 23's tweeters are crisp and detailed but can't really say that about my fives. It may be just the difference in the 2 way vs the 3 way design and voicing. But you all got me thinking that maybe I should swap tweets from the 23 's over to the 5's just to make sure. FYI recap done a while back. :D
 
skandl said:
Okay I replaced my 23's tweeter (with a proper stock replacement) but never got rid of the original. Just want to make sure I am reading this correctly!

The wire in question is the on the front of the tweeter.

1) remove the screen and look at the fine wire going to the cone.
2) daisy chain broken wire with fine copper wire then solder

Does anyone have any pics to clarify if possible I would like to save the tweeter rather than let it collect dust.
Click to expand...

Do a google AK search. This topic has been covered well with lots of pics.
When I was restoring my first pair of model six's, I had dead tweeters after the recap. I replaced them. I opened up the dead ones seeing if the wire was broken, tried to fix it, but no luck for me.
On my second pair of six's, a tweeter went several months after the restoration. Again, I just replaced it. I've kept the original and some day will see if it's repairable, but these are fragile and I try to keep a few on hand.

Glenn
 
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