'68 K-horn refurb complete

[jhawk92]

I wanted to get my initial thoughts down on BEC's work to bring my 36 yr old K-horns back up to "factory fresh." I learned of Bob's work here on the forum several months ago and started to correspond with him via email about his philosophy was on upgrading networks. Since I had been extremely pleased with the sound of my speakers so far, he recommended refurbing the Type A crossovers to get them back up to spec before I try any other mods. This made sense to me as Bob said the caps in the networks tend to drift over time, so what I was listening to would most likely not be what they sounded like from the factory. We also discussed diaphragm replacement on my tweeters as I think I had one that was at a lower output than the other.

We kept in touch and I finally made the decision last week. I was going out of town for a short vacation, so having the K-horns torn apart wouldn't really bother me. Thanks to some great help over in the 2-ch forum, I got the networks, K-77Ms, and K-55V drivers removed and packed up to ship to Bob. We decided to check and see if the K-55Vs would need a diaphragm replacement as well, but they still sounded ok.

Attached is a pic of the original stock crossover.

[jhawk92]

Here is another view of the original crossover. These '68s are in great shape with very little wear and tear.

[jhawk92]

So, off they went to Bob. He called me last weekend to update me on the status. Turns out the caps were down only about 5%, which is much better than others he has tested. He still recommended replacing the caps, and I agreed.

The K-77Ms did need new diaphragms, and Bob said these were ones he had never seen before, due to a difference in construction to "other"K-77s. Bob can explain this in better detail than I can. He also said that during testing, he noticed the tweeters had a slight difference in volume. He spent some time troubleshooting and ended up swapping the magnets which made them nearly identical in output.

The K-55Ms turned out to be in perfect condition. Bob goes into detail in another thread, so I won't dwell on it here. But I really appreciated his phone call with that info, giving me the choice of whether or not to replace the diaphragms. I did not, so Bob packed things up and sent them on their way. This is a pic of the crossover with the three new capacitors on-board.

[jhawk92]

I got home from work this evening to the pleasure of a big box from Arkansas. After some initial work to swap out one of the K-400 horns with a K-401 proved unsuccessful (see my thread on that subject also here in Updates and Mods), I got down to installing all the components.

Things went together pretty well, and soon I had the K-horns tucked back in their corners, ready for their unveiling. I turned on the Scott 299B, and put on a CD. Even though the amp was not warmed up, I could tell an immediate difference. The mids and highs were crisper and cleaner and the one tweeter that seemed lower in output was perfect.

I sat back in my sweet spot and just listened with a big grin. The phantom center was perfect and the vocalists were in the room with me, dead center! Before, the left speaker was slightly overpower the right, so I didn't have the best imaging. Now that was gone and things sounded better than ever.

According to Bob, the caps were up to 0.5 ohms in Equivalent Series Resistance (ESR). Not as bad as some he's seen, but certainly well above 0.02 ohms for a new one. I can certainly agree with the philosophy that replacing the caps in older speakers like mine gives a very good bang for the buck.

I'm glad Bob recommended refurbing my Type A crossovers rather than getting a set of his Type A/AA boards. I was pleased with the Type A before, and now I like it even better. I don't want to start a flame war, but I don't see any need to try anything else in terms of x-overs. The new diaphragms in the K-77s are certainly a good investment as well. Bob said that vintage ones like mine had aluminum voice coils and the phenolic diaphragm was not as consistent thickness as they are now. That, plus the ability to use copper in the voice coils for better conducting and increased power capability makes replacing them a no-brainer.

So, overall, I am very pleased with what I am hearing so far. I will certainly listen a lot more over the next several days, but things sound wonderful. I would like to take this opportunity to thank Bob for a great job. He is certainly an asset to the forum and I'd highly recommend folks with older speakers like mine to look into these easy tweaks. The performance change is well worth it.

[jhawk92]

Nuts, missing photo...

[Frzninvt]

Now you got me thinking about the K-77 & K-55V's in my '62 Cornwalls, maybe they could use a look-see. Maybe a refurb may be in order after 42 years of service. I did notice when I took the back off one that the rubber seal on the back portion of the K-55V had cracks and was dry, not sure if it means anything but they still sound great and I have no channel level difference that I can hear.

[sunnysal]

congrats jhawk! I am pleased to hear that you managed to up your level of listening pleasure once again. regards, tony

[jhawk92]

Frz-

I would sure look into it. I thought my 36 yr old K-horns were sounding good, but replacing the caps and the diaphragms made them even better. My caps were only about 5-7% out of spec, so yours could be at least that different.

Bob's explaination of the different materials for voice coils and diaphragm materials makes sense to me, and why not do that tweak? It costs very little in terms of potential gains. Think about it; how many times has the voice coil been exercised in just a year, let alone 36yrs for mine or 42yrs for yours? All mechanical things can wear out. Klipsch sounds good, so why not let them perform at their best?

Tony-

Yeah, it was a pretty amazing difference; one I could hear almost immediately. I was a bit skeptical that I would be able to hear a difference, but within the first few notes, I knew the changes were good and worthwhile.

I am not sure which change made the most difference; cap replacement, diaphragm replacement; or matching up the magnets. I do hear a bit more hiss through the speakers when the Scott is on and before I spin some music. So I know the cap change has had some impact in terms of letting all the sound come through. K-horns certainly reveal any flaws in your upstream components.

Matching the magnets has certainly helped in terms of overall balanced output levels, and that definitely increases my enjoyment. There's nothing like closing your eyes, enjoying the music, and then opening them and realizing the artist isn't there with you in the room.

If I had to hazard a guess, I'd say the cap replacement has provided the biggest improvement, since that has an effect on the entire spectrum. Maybe Bob could throw his two cents in?

[BEC]

In general, I think cap replacement in old crossovers just should be done. I think if they are twenty or more years old, you would see an improvement, mostly in the higher frequencies, after replacing the caps. The caps develop a resistive component that is age related and start to act like a significant resistance in series with the drivers after some age. I will not go into much here on what type of cap to use. That subject has been argued to death on the forum in other places. I think you get most of the improvement possible with most any good cap. I personally like the GE oil filled cans that I am using. I like the fact that they are an industrial grade component and I like how uniform they are in testing.

I will talk here a bit about the old K-77 tweeter diaphragms. The tweeter construction of the K-77 changed over the years. The ones in Jhawk's 1968 Khorns were some of the early type. These had a construction that used a sort of "diaphragm sandwich" meaning that the diaphragm is glued in between two thick gaskets and it's voice coil is centered in the magnet gap by the 4 holes in the gaskets. That is the style used in the earliest EV T-35s that I have seen. This would be fine if the diaphragm was still available as a pack with gaskets. That is not, however, the case. Now one has to carefully separate the old diaphragm out of that glued together pack and glue a new diaphragm in its place reusing the old gaskets. The first time I saw one of those, I almost did not attempt it because I thought it would be impossible to ever get the diaphragm centered in the magnet gap. I did work out a method to do it and have been successful on dozens now.

Sometime around 1968, a light bulb went off in the head of someone at EV and a brilliant change was made to the tweeter construction. They at that time machined a recess in the diaphragm mount of the tweeter that perfectly centered the voice coil (using the outer circumference of the diaphragm) in the magnet gap. That made diaphragm replacement a snap comparatively and I guess saved EV some money on gaskets and made diaphragm construction easier.

The diaphragms themselves changed in construction around that same time with an improvement in uniformity between diaphragms and use of copper for the winding instead of aluminum. The ones I removed from Jhawk's tweeters had an actual measurable difference in the thickness of the phenolic between the two. One of them measured 0.003 inches in thickness and the other measured 0.0025. That doesn't sound like much but is a variation of around 20 percent in thickness. New ones are a very consistent 0.003 inches in thickness.

I guess the next change worth mentioning happened in 1979 with the advent of the ceramic magnet K-77M. Besides the magnet changing, the diaphragm housing went to a plastic injection molded piece which was meant to be replaced with the diaphragm. It still retains the recess mentioned earlier and the diaphragm can be replaced in the plastic housing but great care must be taken to keep from melting the plastic housing while soldering to the terminals the go through the plastic. These plastic housings are still available (from me at least) now and for some time in the near future. There is available some finite number of these and I don't know what that number is. The tooling to make them is gone and when the existing ones are used up, that is it, unless someone decides to spend the money for another injection mold die. That is many thousands of dollars and my current supplier does not think he would ever recover the cost of that die. And to answer another question that perhaps nobody would ask, yes, the newer plastic housings can be used to replace the old metal ones and that even includes the earliest types that used the "diaphragm sandwich".

Probably more than most wanted to know.

Bob Crites