KLH Model 6

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Is vintage better than the newest gear? Can old be made better than new?

The KLH Model 6s I came across were definitely not better than new when I got them.

They looked OK from the outside – the cabinets and veneers were in decent shape with no gouges or chips, only some water damage. The grilles were complete but the weave was sagging. Inside drivers in both cabinets looked complete and untouched. I purchased the set from a nice older gentleman who had bought them new along with a wheezy Pioneer SX-727 receiver. He was moving into an assisted living facility now and didn’t need the big speakers. For some reason he held on to the receiver, however.

Water-damaged KLH veneer. Soon to get all better

Water-damaged KLH veneer. Soon to get all better

I got the speakers home and plugged them in – they were in the garage at the gentleman’s home and I didn’t have a chance to test before purchasing.

Unh. What a disappointment.

Muddy and veiled. Is this what people raved about?

I’d had my eye on a pair of vintage KLHs for a long time. The early KLH model series, including the 5,6,7,9,17,22/23 and many more, were designed by Henry Kloss, a legend in hi-fidelity design, who also led the design of some of the best-regarded stereo speakers in the 50s, 60s, and 70s at companies like Acoustic Research, Advent, and Cambridge Sound Works. I’d read that the Model 6 was what he considered the best two-way stereo speaker on the market at the time, and an amazing value.

I’d read descriptions of the sound that placed it as well-detailed, extremely pleasurable, and vintage. Folks raved about them, while noting that the tweeter, which reaches pretty low in the spectrum to pick up from the 12″ woofer (effective size is actually closer to 10″), does not go as high as modern tweeters.

Was this the sound everyone was raving about? If so then count me out.

The early models of the 6 had the woofer and the tweeter epoxied right to the cabinet and they cabinets were glued shut, making repairs all but impossible. My set, thankfully, were a later (1972 vintage) model with drivers screwed into the cabinets. I pulled them open to see what I could see.

KLH 6 with removable drivers

KLH 6 with removable drivers

The crossover was pretty simple – a few resistors glued to the backing plate with three capacitors hanging in between the drivers, with a lot of nasty fiberglass insulation thrown in for good measure.

I read a lot more online and found out that these KLHs were notorious for having failing caps in the crossover system which could render the tweeter inoperable. Sometimes new caps were all that was needed to bring things back to life, other times the failed cap created an open circuit which blew the tweeter.

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I soldered in new capacitors in both speakers from Parts-Express (standard Daytons) and put everything back together. One speaker sounded amazing, the other not so. I had a dead tweeter on my hands.

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6 with its innards out

 

Crossover. Couldn't be simpler.

Crossover. Couldn’t be simpler.

 

Nasty fiberglass batting. Use gloves to pull out.

Nasty fiberglass batting. Use gloves to pull out.

A nice gentleman on the Polk Forum sent me a replacement tweeter he had sitting around and I mounted it. In testing with the new caps in I finally understood what everyone was talking about. These sounded great! Vocals were clear,  airy and lifelike. Guitar notes shimmered and hung. Bass was big, real big. The only issue I could find is that sometimes the sound would get ‘boxy’ or constricted sounding in mid-heavy passages – the point where the band starts in ‘Wish You Were Here’ is an example. Perhaps this will go away when the caps burn in more. Otherwise I couldn’t have been more happy.

I was amazed at the size of the sound coming out of a two-way speaker of relatively modest size. These aren’t huge cabinets – 11″x23″x12 but they sure can put down the bass. I’ve read that more bass comes from properly sealing the cabinets and making sure that the cloth surrounds on the woofer are doped with a sealant. I put moretite on the drivers before replacing them, which I think will help. Since I’m happy with the bass response from the speakers I won’t attempt re-doping the woofer surrounds at this point. It seems that there is a risk of ruining the frequency response of the speaker if you don’t do this right so I’ll leave them be.

Not long after I screwed the speakers back together I noticed a buzzing sound from one. Using test tones I isolated the buzz to the lower registers of the tweeter, around approximately 1200 hz, with a return higher up the register. The buzz only came from the replacement tweeter. What a shame. The second tweeter to die. Judging from the amount of information online from folks with dead tweeters I began to wonder if these 40 year-old tweeters were a weakness and prone to failure. Looking on Ebay made me realize that they are pretty expensive ($30 per), and since I already had a lot sunk into these speakers, I didn’t want to take another risk. As an experiment, I ordered some phenolic ring tweeters from Parts Express which are billed as exact replacements for tweeters in classic 70’s 2-way speakers, including Realistic, Marantz, and Acoustic Research. They sure look identical to the KLH tweeters, once you have taken the metal grid off of them. Their outer flange is smaller so I had to fasion an adaptor out of wood so they will fit the larger opening of the KLH 6. I’m hoping having them another 1 cm forward of the original tweeter placement won’t introduce any phasing issues with the woofer. I don’t think it will since I’ve seen that over the years the tweeter placement depth on the 6s changed a little. If my experiment is successful I should have a restored KLH with perhaps improved high frequency properties. Of course purists will not be happy, but if the sound is right who cares? And if it doesn’t work my modifications are fully removable and I can spring for another original KLH tweeter on eBay.

Update – I just installed the tweeter. So far so good. Tone-wise I can discern no difference whatsover from the original functioning tweeter in the other speaker. Perhaps there is a little more presence or volume but the difference is so minute I can hardly tell. I ran test tones through both speakers and there was no buzzing or other bad behavior. I think I will do the other one with the new tweeter to have a matched set just to be safe.

Modified KLH with replacement phenolic tweeter from Parts-Express. Everything works fine but the grille won't fit snugly over the adaptor the way I have it cut. Will have to work on that.

Modified KLH with replacement phenolic tweeter from Parts-Express. Everything works fine but the grille won’t fit snugly over the adaptor the way I have it cut. Will have to work on that.

 

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~ by silverfacestereo on December 29, 2012.

6 Responses to “KLH Model 6”

  1. The replacement tweeter came in both 4 and 8 ohm versions. Which did you select?

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  2. can iuse klh model six tweeter to replace my tweeter model 17″ klh

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  3. What were the specs of the replacement capacitors you used? I just picked up a pair of these on the cheap from my local thrift store, and on one the tweeter is completely non-functioning, and the other sounds on its way out as well. I just bought a pair of working KLH model 6 tweeters on eBay to swap out, but don’t want to do so until I have the caps sorted out. Your help would be greatly appreciated!

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    • I think that I used 2 2uF caps in parallel and an 8uF cap, but don’t remember for sure. Crossover schematics should be available online, and when you open up the speaker the caps should be labelled. Good luck!!

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