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RTally

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  1. The back of my KLH Six is labeled 8 ohms. I assume that means the tweeter has nominal rating of 8 ohms. If you replace an 8 ohm tweeter with a 4 ohm tweeter the crossover frequency will double for a first order filter such as used in the Six. If you do not change the cap values, you will end up with a hole in the frequency response between the woofer crossover frequency and the new tweeter crossover frequency. That is, the woofer will roll off at its original 1500 Hz crossover frequency and the tweeter will pick up at 3000 Hz, twice the woofer's crossover frequency. When replacing drivers, if an original, OEM driver is not used, the replacement driver should match the original TS parameters as closely as possible. If you do not want to rework the crossover, you need to at least match the driver impedance at the crossover frequency.
  2. The thicker conductor is the tinsel and connects the woofer terminal to the rivet that is supposed to be in the cone. Tinsel is very flexible and is typically a braided conductor with many very thin strands. The thin wire from the rivet extends to the voice coil (VC) and is the lead from the VC. The VC lead should be attached to the cone between the VC and the rivet (that is the purpose of the thin black line of stuff on the backside of the cone).
  3. I don't understand the resistance to using the proven doping compound made by RoyC. It is not expensive. It works very well. And it is readily available. Using grease to seal a surround sounds like a bad idea to me. Grease, even thick viscous grease, will not stay on the surrounds when the woofers are played loudly. The rapid, back and forth movement of the cone edge will through the grease off the surround. I cannot imagine the mess that grease would make, both inside and outside the cabinet. And if anyone ever wanted to seal the surrounds correctly, that grease would not be fun to remove. Either use the correct stuff or leave them as they are. If you do not want to improve them, leave them be.
  4. If I were to buy a replacement woofer from someone else, I would want assurance that either the surrounds are as original (never been redoped) or that only the good stuff was used (RoyC's or vintage-ar). Too many people have used Permatex, PVA glue, and other crap to seal the surrounds. If the wrong stuff has been used, the woofer will have a higher Fs, changing the way it sounds. You cannot tell by color. As others have noted, the original woofers sometimes had black surrounds. My pair of 20's have black surrounds and they were original.
  5. RTally

    12.5 question

    KLH cloth surrounds are generally either brown/tan or black. I believe that the black surrounds were that way from the factory and just had carbon black added to the doping material. RoyC's goop will work on either type. I know 'cuz my KLJ Sixes have brown surrounds and my Twenties have black surrounds.
  6. Every woofer I have refoamed (dozens) have sounded better after several hours of use. My experience is that foams loosen up and go deeper with use.
  7. When doing the push test, after you push in, hold that position for at least 10 seconds so that the air pressure stabilizes. Then quickly release the cone to see how long it takes to return to resting position. One second or longer to return is good. Less than 1/2 second indicates air leakage, either through the surround or elsewhere.
  8. I am firmly in the camp of using a tone to magnetically center the voice coil. The advantage is you do not have to mess with the dust cap - no cutting out the dust cap, no gluing it back in. For the tone method, use a tone generator (I have an app on my phone) and play a 30 to 40 Hz Hz tone through the driver. Play the tone only loud enough that you can feel the cone move. I glue the inside of the surround to the cone and let it dry. Then I attach the leads from my stereo to the driver and get ready to play the tone. I glue the outer edge of the surround to the basket and then play the tone as I press the surround edge in place. Using Aleene's glue, I have a couple minutes to mess around with the cone and surround to ensure all is well. Before the glue sets, I turn off the tone and then play with the cone. Push it in evenly and see if you can hear or feel any scratching. Press on each side and see what you notice. I do this so that I can learn what happens when the cone is not centered. I then play the tone again to ensure the VC is centered while going around the edge of the surround to ensure it is seated and the glue is starting to cure. When I am satisfied, I turn off the tone and let the glue cure. Sometimes I clamp the surround to the basket to hold it in place. Other times I just keep pressing around the surround until the glue dries. Aleene's sets up in about 5 minutes. After the glue is cured, press the cone evenly around the VC to ensure there is no rubbing. I've done dozens this way and have never had a problem. You are done.
  9. Do the push test. Push in the woofer, hold for several seconds, and then quickly release. See how long it takes the cone to return to its normal position. Generally, anything over about 1/2 second is fine, with the better sealed speakers taking more than a second to return. If the cone pops back too quickly, you have a leak somewhere, either the surround or elsewhere.
  10. I have two pair of Dynaco A25 speakers. Three of the four speakers have the port on top. I have seen references to this version being called A25X, not to be confused with the A25XL.
  11. Mortite, as Aadams, points out above is commonly used. Many of the vintage speakers I've rebuilt have used something similar. I generally replace the original with fresh Mortite and I get a good seal on my drivers. It is readily available almost anywhere.
  12. Most times the glue in vintage speakers is easily lifted with a putty knife. At least, that is all I needed for dozens of speakers. I use the edge of the putty knife (a steel one, not plastic) to get under an edge of the glue and pry up. If the glue is hard, it cracks and comes away in pieces. Or if it is a bit soft, it pries up in on big piece. The alternative is to leave the glued parts in place and cut the leads. I solder new caps either to the left over leads or to their terminating point, depending upon which has easier access.
  13. RTally

    KLH 17 schematic?

    Does your Seventeen match this schematic? It is best to replace the caps with like-for-like values. Redesigning a crossover is not a trivial task. The KLH 17 crossover is not a simple first order filter. It is a 3x cascaded, first order filter that has a switchable FR for the tweeter. Each position of the switch has a different contour for the tweeter FR. The 3 ohm resistors in parallel with the 2 uF caps allow a portion of the signal to bypass the cap and has the effect of lowering the attenuation at higher frequencies. The frequency at which the attenuation changes and the amount of attenuation is a function of the switch position.
  14. You should be able to post pictures as long as they are no more than 100 kB in size.
  15. RTally

    hello

    Welcome to the forum. I hope you find all the information you seek.
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