KLH 6 speakers

[Guest violin]

Andy,some months ago you answered a tread from someone about how to get into the cabinet of a KLH Model 6 speaker. I think that you told them that the speakers below serial number 30,000 were all epoxy glued and were next to impossible to get into without destroying the cabinet.

After your answer two days ago to my question about correct hook-up of the pair that I just got,I listened to them and the tweeter is gone in both speakers.I do not know if it is in fact the tweeter or the capacitors. The woofers play with no problems. After examining these speakers, I see no way to get into them either. Their serial numbers are 061256 and 076656. Do these later serial numbers indicate any improved chance of being able to get into the box that I am not aware of or are all of these speakers the same way?

At least if I have to throw them away I only have ten bucks total in them.

Your comments are appreciated.

Regards, Carter

[Guest Feighner]

I'm looking at the circuit diagram of my earlier six's and they show all 3 caps as oil filled so it's doubtful they could fail. Kloss told me that the reason he put them in was because he wanted the caps to outlive the buyer since they were sealed in. On the other hand he used elec. caps on the 17's because they were accessible by removing the woofer. I had one fail about 30 years after he gave them to me, that's how I know.

[Andy]

The Model six was introduced in 1958 with both the tweeter and the woofer being a sealed in epoxy type. The only way into the cabinet is to either pry the front baffle board out or cut out some sort of hole to get to the electronics. If the drivers are blown, you'll have to do some serious reconstruction of the speaker structures. In the early 1960s, KLH changed to a screw in tweeter making service a little easier, but not much. Then in about 1965 at about serial number 92,000 the standard screw in woofer was added making all repairs easy fom this point forward.

I have a pair of Model Sixes, serial numbers 0684 and 0711 which dates them to March or April 1958. They sound like new and I dred the day something goes wrong since they're the epoxied type. One of the nicest features on these is the cabinets which are 12-ply marine plywood with a blond corina finish. KLH only used this exspensive plywood for several months.

[soundminded]

>Andy,some months ago you answered a tread from someone about

>how to get into the cabinet of a KLH Model 6 speaker. I think

>that you told them that the speakers below serial number

>30,000 were all epoxy glued and were next to impossible to get

>into without destroying the cabinet.

> After your answer two days ago to my question about correct

>hook-up of the pair that I just got,I listened to them and the

>tweeter is gone in both speakers.I do not know if it is in

>fact the tweeter or the capacitors. The woofers play with no

>problems. After examining these speakers, I see no way to get

>into them either. Their serial numbers are 061256 and 076656.

>Do these later serial numbers indicate any improved chance of

>being able to get into the box that I am not aware of or are

>all of these speakers the same way?

> At least if I have to throw them away I only have ten bucks

>total in them.

> Your comments are appreciated.

>

>Regards, Carter

I've got KLH 6s with three different types of factory construction. It is almost certain that the original capacitors have failed. This is by far the most common problem with this speaker. When that happens, the tweeter won't operate at all. The original capacitor was actualy two capacitors in the same housing in parallel and can therefore be replaced by a single capacitor. It is in series with the tweeter and I think it is 8 microfarads. Get one which is non polarized and rated for at least 50 volts. 100 volts is more commonly available. I used the cheapest kind out there from Parts Express and I think they are under $1 each. You can get more exotic if you want to with polypropylene capacitors of various manufacture, I'm not going to get into the controversy now over whether or not it matters.

The earliest types had the woofer and tweeter epoxy cast into the front baffle board. I have a pair like this which were serviced at the factory when it was in Cambridge many many years ago. If I need to fix it again, heaven help me. I would probably try to chip away the wood from behind the front of the tweeter flange and then repair it with wood filler and silicone to restore its air tightness after it is repaired. The grill cloth in this early version is not removable without destroying it. If you have this type, you will have to pull it off and sacrifice it. The front face of the tweeter is square sheet metal with corners cut at 45 degrees. Feel it through the grill cloth. If it is perfectly flat, you have the epoxy cast type. If you feel a slight bump at each corner, you are in luck, it was screwed in and can be removed easily once the grill cloth is removed. I've got one like this and I will make a new grill cloth from open weave fabric, some masonite, and some velcro. Later versions have this type of grill cloth already and it is easily removable without damaging it by just prying under the edges and pulling it away. Be careful when soldering the replacement capacitor not to damage the lead from the tweeter terminal to the voice coil. I would not try to gain access to the tweeter from the back of the cabinet. BTW, you can work through the opening in the front baffleboard once the tweeter is removed, it's a large enough hole for me to easily get my hand into the fiberglass. There was enough wire for me to get the attached capacitor through it to the outside.

To finish restoring the functionality of this speaker, consider applying a material similar to XL-49 sealant to the woofer surround. This can be obtained from Orange County Speaker Company for around $10. Their number is 800-897-8373 and 714-554-8520. The surround will not deteriorate since it is made of cloth, not foam but it will become porous over time and needs to be resealed or the enclosure will not be air tight and you will not get satisfactory bass. Some people have foolishly used other materials which cured somewhat hard and compromised the compliance of the surround and therefore the bass.

This is a very good speaker when it is performing as intended and is worth restoring. Good Luck.

[tysontom]

>The Model six was introduced in 1958 with both the tweeter

>and the woofer being a sealed in epoxy type. The only way into

>the cabinet is to either pry the front baffle board out or

>cut out some sort of hole to get to the electronics. If the

>drivers are blown, you'll have to do some serious

>reconstruction of the speaker structures.

>

What KLH did at the factory when a repair was needed to the epoxied-in drivers was to: (1) rip out the old grill cloth, (2) remove the woofer cone and voice-coil assembly to get access into the cabinet and (3) make the necessary repairs -- then finish with a new woofer moving assembly and grill cloth. As someone commented, the grill cloths were more or less permanently tucked and glued into the edge of the cabinet, so it is not feasible to save the grill this way. Repairs could not be done in the field, and this was a big problem.

Although the expoxied woofers were stellar performers, I suspect this obtuse method of epoxy construction cost KLH a lot of money in the long run, and this may be the reason that KLH did not have the long and basically "no-fault" warranty that some other companies had. The KLH Four, KLH Six and the KLH Seven were constructed in this manner, and many tens-of-thousands were built, and warranty-repair costs must have been prohibitive.

Henry Kloss had a tendancy to make devices overly complicated. In 1954, Kloss was somewhat stumped over a method of mounting the AR-1 woofer in the new special-made AR-1 sealed cabinets. He was the man who pioneered the method of gluing the backs of the cabinets in place rather than screwing them on, and this presented a problem in how to mount the woofer to the cabinet. Traditionally, speaker companies always mounted drivers from the *back* of a cabinet, with only the cone showing through the speaker hole. Since access to the rear was now denied, Kloss was trying to engineer a method of jigs and clamps that would "pass the speaker through an oblong hole in the front of the speaker, turn it around to face the front and then screw it in place." The oblong hole had to be patched to make it simply round, once this operation was finished. Ed Villchur suggested that he mount the speaker to the front by recessing the flange, using Mortite to seal it and screwing it to the front (the way we now know it). Villchur also suggested using T-Nuts and machine screws.

--Tom Tyson

[soundminded]

I bought a pair used from a private party in 1964. They were utility cabinets painted brown. The tweeter on one didn't work. I called the KLH factory and they shipped me a carton for $5. I think it cost about $10 to ship it to them UPS. They repaired it and shipped it back at no charge and apologized for the failure. I have never been so impressed with customer service in my life. I don't know how they managed to repair it but you can still see where they apparantly inserted a tool between the baffleboard and the cabinet. It left some scratches where the paint had been removed. I always assumed they had pried the entire baffleboard away to get to the inside. The other one of that pair was repaired at the factory as well some years later. I'm pretty sure they told me they had to remove the woofer cone and work through the basket. I also dread the day it needs reparing again. I've got one which has the screwed in tweeter but an epoxied woofer and another which has both woofer and tweeter screwed in.

I've commented in the past about some of Henry Kloss' manufacturing quirks. Clearly a brilliant man and a pioneer, he did seem to have some impractical ideas about how things should be assembled. My experience with an early AR2a I reported on elsewhere here was a case in point, the putty being more like glue even after nearly half a century. I wish he had decided to keep the entire crossover network external to the speaker enclosure, at least the sealed section. This would have set the standard for the entire industry and made all repairs and upgrades to acoustic suspension speakers much easier and cheaper.

[Guest seeya]

Just have one question on these, I have the later model with both screw in tweeters and woofers. both tweeters have no sound. I did a ohm test with tone on a meter and got nothing. Is this a sure test or is there a good chance that the tweeters are still good? If so what a good test?

[soundminded]

If you put your ohm meter directly across the tweeter voice coil after you removed it from the enclosure and it reads open circuit, I am sorry to say it appears to have been burned out. If you measured it with the capacitor still in series with the tweeter, you'd expect to read an open circuit. To be absolutely certain, connect the output of a very low powered amplifier like a transistor radio's directly to the tweeter bypassing the capacitor and if there is no sound, not even a slight crackling noise, I'm afraid the voice coil is burned open. As one last test, try a 1 1/2 volt battery. No crackle means an open voice coil. These speakers like most high quality high fidelity speakers of that era were not designed to play rock music at ear splitting levels. The rated system capacity was only 40 watts. If they were abused, this is often the result you'd expect. You can directly substitute tweeters from canibalized KLH 17, 5, 12, and some other models. They are sometimes even available separately on e-bay. A lot of them were manufactured and sold so it often isn't a particularly hard tweeter to replace if you hunt for them.