This post is being updated as I do different things to repair and refurb a pair of 42 year old Quad ESL-63 electrostatic speakers. Check back every couple days for updates that will be added to the bottom of this post.
I've been a fan of ESLs since I learned about them and started building them myself in Japan back in the 80s. In the early 90s I had acquired a pair of Quad ESL-63s that I repaired and used for a few years. I was always dissatisfied with their mechanical construction- much too complex and flimsy. I don't think Quad ever had a manufacturing engineer look at the design, because it could have been much simpler, more robust, and probably a lot less expensive to manufacture if they had. I designed and built new frames for the drivers from those speakers using t-slot aluminum, but never got around to rebuilding those speakers in the new frames. I still have all that stuff that I may put to use soon. Quad's follow-up to the ESL-63, The ESL989, was more solidly constructed, as are their current offerings.
I recently found a Craig's List deal on a pair of ESL-63s with their shipping boxes. The seller stated one works fine and the other makes noise. The speakers were listed for almost a month in Chicago, where you'd think there would be at least one audio nut willing to take on the challenge of repairs, or to strip them for parts to sell on ebay. Apparently not. After seeing them listed for a month, I decided to check them out.
Outwardly, they are in perfect physical condition, indistinguishable from new, except both were missing the original plastic feet and a couple screws from the bottom covers. Not bad for speakers made in 1983. You can learn all about Quad ESLs (the original ones, and the 63s) here. Here are the owner's and service manuals for the ESL-63.
There have been many reviews of this speaker over the last few decades. Start with Stereophile, here. And here.
Owner reviews here.
Some info and specs here.
Another review here.
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| ESL-63 on the left, next to B&W 703 S3 on the right for size comparison. |
I handed the man $300 and took them home. Thanks Tom! I assumed that I was going to have to work on them, so there wasn't much point in testing them before I bought them.
When I got home, I tested them. Sure enough, one works fine the other makes noise. Even though one is working, both will need some work to ensure reliable (is that possible with ESL-63s?) operation for the next several years.
I started the usual way- replacing the electrolytic caps. There are exactly two in each speaker. A 1000 uF 16V cap on the power supply for the arc sensor, and a 220 uF nonpolar electrolytic input coupling cap.
Accessing the caps is done through the bottom of the speaker. I turned it upside down and leaned it against my work table and removed the screws holding the bottom cover in place. On the inside of the bottom cover there are two strips of foam tape that have rotted and will need to be replaced. This foreshadows MUCH more to come...
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| Rotted foam tape inside the bottom cover. It only contacts the PCB in the chassis in two small areas, so I'm not sure why they used such long pieces of tape. |
I ordered new caps from Parts Express- 220 uF nonpolar electrolytics, and a pair of Audyn 4.7 uF PP film caps to bypass them, and while I was waiting for delivery, I printed new TPU feet for the speakers. When the caps arrived, I went in to install them.
That's where I ran into the first problems. In the first speaker (the one that worked), the 220 uF cap's solder connection to the input terminal had failed and it was making contact only by the strength of the spring force of the leads! I also found a black ground wire that was supposed to be soldered to a lug, just left floating in the air. Oops!
The PCB that the caps both mount on is held in the enclosure by two + head screws. Those screws are at the bottom of the enclosure, making it almost impossible to remove them to release the PCB, even with a right angle drive wrench and screwdriver bit. Fortunately, there's enough room to get a soldering iron in without removing the board, so I was able to remove the old parts and install the new ones with minimal effort.
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| Bottom of one of the speakers with the cover removed. The nonpolar cap is the blue part located under the cement resistor, circled in green. There's plenty of room for the replacement caps I ordered. The only thing supporting the cap is the wire that wasn't properly soldered to the input connector and that thin yellow wire that's going to the PCB. Hmmmm. Not what I would expect in a very expensive speaker. Note- the empty space to the right of the green circle would allow for much larger film caps to be installed in place of the non polar electrolytic caps I used. |
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| Input board screws. Now I'm starting to remember what my ESL-63s were like back in the 90s- a mechanical nightmare! The white wire is the antenna for the arc detector. I had to unsolder it to get to the solder pads for the input and 1000 uF caps. |
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Unsoldered ground wire. Not really a big deal- it's one of two wires that ground the aluminum bottom cover of the speaker.
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| After I removed the old input coupling cap and resistor you can see the 1000 uF cap on the input board. |
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| New input coupling caps installed. The new 1000 uF cap is under there, too. I was able to unsolder the old parts and solder in the new parts from the bottom side of the PCB without having to take the board out of the chassis. |
I had forgotten what a PITA these speakers are to work on. My intention with this blog post was to get to the driver fix(s) quickly and get the thing working again, but as I got deeper into the speaker, I found a LOT of different foam and other tapes that had rotted away. I spent 3 days cleaning the old tape and adhesives off the different parts, replacing it with new stuff that I chose to hopefully last longer than the original stuff.
Keep in mind, that everything I am doing to replace rotted foam tape in the first speaker will also have to be done to the other speaker. The speakers won't work reliably without replacing all that tape- some of it is inside the dust covers. In all, I spent about $100 on all the tapes, solvents, and glue supplies needed to fix both speakers.
Accessing the drivers
The driver enclosure consists of two vertical aluminum rails, plastic top and bottom plates, and four vertical aluminum support rods, two in front and two in back, all bolted to the electronics chassis.
The speakers are covered by cloth "socks" attached to the frame by hook type tape on the top of the driver enclosure. Behind the sock there are metal grids on the front and back side of the speaker that provide some mechanical protection for the drivers and keep curious fingers away from the high voltage inside.
The step by step procedure to gain access to the drivers is to slide the top wood cover to one side and lift it off, then release the sock from the hook tape and slide it down on the speaker frame. Next, peel off the tape holding the metal grids at the top and bottom of the frame and pry them free of the crumbling foam tape that holds them to the top and bottom plates of the driver enclosure. Then pull the thin wires out from the vertical edges (apparently used to fill the space in the aluminum side rails), and remove the front and rear grids. Finally, snap the frames holding the dust covers off the speaker frame, slide them out sideways, and set them aside.
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| Sock attachment at the top of the speaker with the wood top cover removed. There's hook tape under the sock holding it in place. |
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| Hook tape on top of the driver enclosure. |
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| Gooey adhesive under the hook tape. |
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| I found the best way to remove this stuff was to start by rolling it off instead of scraping it. |
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| Adhesive booger removed from the top of the driver enclosure. This was the stickiest, gooiest, stuff I've ever seen. |
The metal grids have what looks like duct tape covering the vertical edges, and are held in place by more tape along the top and bottom edges, and by double sided foam tape also at top and bottom, and on two vertical supports near the center of the speaker, front and back. All that foam has rotted, and all the tape's adhesive has dried out, so all of it has to be removed and replaced before putting the speakers back together. It's a tedious and messy job.
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| Front upper left corner of the speaker with the sock pulled down. The metal grid with duct tape on its vertical edge fits into slots in the vertical aluminum frame pieces. The grid is mounted using double sided foam tape at the top and bottom. The green wire fills up the space inside the vertical frame piece so that the grid can't rattle. It is removed by simply pulling it out. |
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| Front upper left corner showing grid coming out of the frame after it has been released from the foam tape. You can see the two vertical supports to the right, just behind the grid. |
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| Front grid removed from the speaker. Gaffer's tape still on the edges. Residue from the rotted foam tape visible along the top and bottom edges. |
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| Brown foam tape residue on the back side of the front grid. This is easily cleaned off with a wire brush. The duct tape at the vertical edges of the grid will also be removed and replaced. |
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| Front bottom left corner of the speaker showing rotted foam tape and residue from the duct tape that held the front metal grid in place. |
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| Front top edge of the speaker showing foam and duct tape residue. One of the two vertical supports (black) is visible at the center. |
 | Poorly positioned duct tape on the edge of the metal grid. That will be replaced, and positioned properly.
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| Rotted foam tape on one of the four vertical supports. You can see light reflecting off the wrinkled dust cover behind the support. |
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| This is the scraper I use- it has a VERY sharp edge, so be careful! After scraping, I wipe everything with Goo Gone, Goof Off, or IPA, to remove the adhesive residue. Goo Gone is reserved for parts I can completely remove from the speaker and wash with detergent in a sink after (you have to wash the orange oil off). |
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| Scraping the rotten foam tape off one of the two vertical supports. |
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| Scraping the rotten double sided foam tape off the top edge of the speaker. The duct tape residue has already been scraped off. Why is this tape needed at all? The top and bottom of the grids are secured with duct/gaffer tape wrapped all around the driver enclosure. |
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Front bottom of speaker showing the mess created when scraping all the tape residue off the speaker. I keep a vacuum cleaner handy and vacuum this stuff up. You can see the two vertical supports near the center of the speaker.
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| Wrinkles in dust cover. This is bad, but easily fixed. The wrinkles will cause rattling noises. This will have to be tightened, if I can get it off and back on again without breaking it, or it will have to be replaced. When it's back on the speaker, there should not be any wrinkles. The dust cover is double side taped to a plastic frame that snaps onto aluminum side pieces and plastic pieces at the top and bottom of the speaker frame. |
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| Back side of the speaker with the grid off- requires the same foam tape cleanup as the front side. You can see the dust cover is badly wrinkled here. The dust covers just snap off the frame and slide out to the side of the speaker. |
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| Dust cover removed, you can see some foam tape hanging down on the driver grid. The black piece is where the dust cover snaps onto the top edge of the speaker. Note- that foam is inside the dust cover- as it rots, it crumbles, and can get inside the drivers and cause all sorts of noise problems. |
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| Bottom corner showing the black piece where the dust cover snaps on, and foam tape. The wire spring like thig is there to ground the aluminum frame pieces and the steel protective grid (already removed). |
Removing the drivers
First you'll have to take out the dust covers. Start at a corner and work your way around, snapping it off the driver enclosure frame as you go. Once the whole dust cover frame is loose, slide the cover out sideways. Set them aside where the film will be safe.
Each speaker has four drivers, two for bass (there's no crossover, but there are resistors in series with the bass panels that interact with the panel's own capacitance to roll off high frequencies) located at the top and bottom of the speaker and two centrally located drivers that are divided into rings that are fed by a delay line to simulate a pulsing spherical radiator. The drivers can be removed without taking the top of the frame off. The procedure is to unsolder the wires from the drivers, then unscrew one of the middle drivers and take it out out of the frame sideways. Then take out the other middle driver the same way, and finally remove the top and bottom bass drivers by shifting them up or down and then remove them sideways through the frame.
note 3/2/25- you may as well take the top plate off - it's easy enough and makes removing the drivers and the dust covers easier. When the top is off, be careful not to apply a lot of force to any of the vertical parts of the driver enclosure.
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| You have to unsolder the wires, front and back, in order to remove the drivers. |
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| This is how you get the drivers out- remove the two in the middle first, then the top and bottom drivers can come out. Each driver is held in by 4 screws that go into aluminum L brackets that run the vertical height of the speaker. Once they are all out, set them aside- there's more foam tape to replace! |
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| The top driver has to be dropped down a bit to get it out of the frame, so you have to remove the driver below it first. The black piece in the green rectangle is the part that the dust cover snaps onto. It comes out with the driver. |
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| This is the top dust cover mount. That rotten foam tape has to be replaced before it falls into the drivers and causes problems. There is a similar piece at the bottom of the speaker that doesn't come out with the drivers. |
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| All drivers removed, the rotten foam tape in the dust cover mount needs to be replaced. |
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| It's a little hard to make out here, but those pieces of foam tape are mounted on an L bracket where the drivers mount. The brackets are on the right and left sides of the speaker. You can also see foam tape that runs the length of the bracket peeking out from behind it. All that stuff is inside the dust covers, crumbling, and has to be replaced. |
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| Here are all the locations of the tapes that need to be replaced. A, C, and D are all inside the dust covers, so it's absolutely critical to clean the old stuff out and replace it with long lasting materials. Double sided tapes are used to mount the steel grids on the speakers and to mount the dust cover film. All others have adhesive on one side only. |
Adhesive tapes for 2 speakers | | | | | | |
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| location | total length | width | thickness | adhesive | type |
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| A | driver mounting brackets | 48" | 3/8" | 1/4" | single | foam |
| B | vertical frame supports | 248" | 3/8" | 1/4" | single | foam |
| C | driver mounting brackets | 120" | 1/2-3/4" | 3/4" | single | foam |
| D | top and bottom dust cover mounts | 184" | 3/8" | 1/4" | single | foam |
| E | inside bottom panel | 8" | 3/8" | 1/4" | single | foam |
| F | top and bottom of frame, holds grids | 200" | 5/16" | 1/8" | double side | foam |
| G | top and bottom of frame, over grids | 234" | 1/2" | | single | gaffer |
| H | vertical edges of grids | 256" | 1" | | single | gaffer |
| J | dust cover frames | 448" | 3/4" | 1/8" | double side | foam/other |
Note: F tape seems redundant- the G gaffer tape wraps around the driver enclosure, preventing the grids from moving. Maybe I'll use some of the same tape used at B and D to prevent the grids from rattling...
Replace the tapes
The procedure with parts that can be removed from the frame is to first scrape as much of the old tape off as possible, then take them to a sink and spray with Goo Gone, an orange oil based solvent that dissolves the adhesive. Let it sit with the Goo Gone for a while then start wiping with a paper towel, folding frequently. Then spray the whole thing again, let it sit a while, then wipe with paper towels again. And again. And again. Finally, when it looks like all the sticky residue is gone, wash the parts with dish detergent and hot water to remove the orange oil.
For parts that aren't coming out of the frame (the bottom dust cover mount), wipe with paper towels soaked with Goof Off several times. Goof Off is very volatile, so use good ventilation. It will evaporate and not leave any residue of its own, but you may have to wipe several times with it to get rid of all the adhesive residue.
I measured the old tape and looked for modern substitutes. I selected some EPDM rubber weather seal to replace most of the old foam tape, as it should last a lot longer than that stuff that was in the speakers. The thick foam tape that goes on the vertical driver mounting rails was replaced with some this weatherseal:
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| Thick foam tape for the driver mounting brackets, C in table above. I bought 1 roll of this stuff. It's 1" wide, so I cut it to the length I need (31") then cut it length-wise so I have two strips that are 1/2" wide. There will be some left over. |
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| Small EPDM rubber foam tape for A, B, D, and E in table above. I bought three rolls of this for the two speakers and will have some left over. |
I also bought some 3/4" wide Scotch brand "permanent" double sided tape to use on the hook tape that holds the socks on the speakers, and for the dust covers, and this 1/4" VHB tape to mount the steel grids. Finally, I also bought some 1/2" and 1 " wide gaffer's tape to mount the steel grids.
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| One of the two driver brackets (per speaker) with new foam tape installed. |
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| Top dust cover mount with new foam tape installed. |
I peeled the tape off the vertical edges of grids and found that the adhesive had completely dried out, much of it turning to dust as I peeled it off. The rest scraped off easily. The foam tape residue was a bit more tenacious. I used the scraper to get most of it off, then used a wire brush to get the rest. Finally, I vacuumed and wiped the grids with IPA.
At this point, I have put in at least 12 hours of labor cleaning up the old tape and its residue and shopping for and installing new tape. That's for one speaker, and I haven't even repaired the driver(s) or dust covers yet. This is why 40 year old ESLs can be purchased cheaply, and why it would be cheaper to buy new ones than to have a pair of old ones professionally refurbished!
I replaced the duct tape on the edges of the grids with 1" gaffer's tape folded over as the duct tape was. I am thinking about whether to use any double sided foam tape at the top and bottom of the grids again as the grids are held in place by gaffer tape wrapped all around the top and bottom of the driver enclosure. Maye I'll just put in some of the narrow brown EPDM foam tape to ensure the grids can rattle and then wrap with the gaffer tape.
The Drivers
Each driver consists of two plastic grids with two stator PCBs glued to them. The grids hold the two stators parallel and about 4.8 mm apart. There's a 3.5 um thick polyester (Mylar, or other brand) diaphragm with a high resistivity coating glued to one of the grids, between the stators, putting it about 2.4 mm away from either stator. The speaker has a 5.25 kVDC bias supply that connects to the stators and the diaphragm. If the diaphragm breaks and contacts the stators, or the stators come unglued from the grids and contact the diaphragm, or some foreign material has found its way between the stator and diaphragm, the driver will make hissing, whining, and popping noises. My bad speaker makes such noises that you can hear, here.
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| Original solder on one of the center drivers. Do you think they used enough solder? The black stuff on the edge is where one of the metal clips was positioned. All the clips had a little rust on them. |
There are three screws and some metal spring clips holding the two plastic grids together. Carefully remove the screws and then the metal clips to separate the two halves of the drivers. The diaphragm will be glued to one of the grids. Look carefully at both sides of each grid. Look for any loose stators by gently pushing on them with your finger tip, and look for holes or tears in the diaphragms and burn marks on the stators. A torn diaphragm, or one that has holes, has to be replaced. Loose stators on the non diaphragm side can be (maybe) reglued without too much effort. However, if the stator is loose on that side, it won't be long before it's loose on the diaphragm side of the driver, too. Plan on replacing the diaphragms if you have to reglue ANY stators.
The best case is that the stator(s) have come unglued, because they can be reglued without replacing the diaphragm. The worst case is that the diaphragm is broken and the stator(s) have become unglued. In that case, the diaphragm has to be replaced, and stators have to be reglued. No, actually, the worst case is that the stator on the diaphragm side of the driver has come unglued and the diaphragm is in good shape. That means you have to destroy the good diaphragm (ugh!) in order to recement the stator, and then you have to replace the diaphragm. Don't worry, it isn't that hard to do.
Upon inspection, I found that all four drivers had some areas where the stators had come loose from the grids. I will be regluing all of them, in both speakers, and replacing all the diaphragms.
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| One of the drivers opened up. The gray stuff is the high resistivity coating on the diaphragm- it's supposed to look like that. The metal tape at the edges of the top part makes contact with the coating on the diaphragm and allows charge to transfer to the diaphragm. You can see a thin cloth covering the stator. That's there to dampen diaphragm resonance. Don't remove it, and try not to damage it. Be careful when unsoldering the electrical connections to the stators. |
Regluing stators
There are couple ways to approach this- you can sacrifice the diaphragms and completely remove the stators from the grids, allowing you to clean off the old glue and reglue them to the grids with all new glue, but that will require replacing all the diaphragms- a tricky process, prone to failure.
Alternatively, you can remove the stators from the grids that don't have diaphragms, clean off the old glue, and reglue them with new glue, and then reglue the other stators with the diaphragms in place. A slightly tricky process, but not nearly as bad as replacing the diaphragms.
If the stators are loose on the diaphragm sides of the drivers, the best/only way to fix them is to remove the diaphragms, reglue the stators, then replace the diaphragms. There's just no good way to recement the stator with the diaphragm in place. In fact, if any stator is loose, it means the glue is failing, and they will all be loose soon. Don't mess around. Reglue all the stators and replace the diaphragms.
I'll be removing the diaphragms and regluing all the stators, using clear polyurethane Gorilla Glue applied with a syringe. Then I'll put new diaphragms on the speakers. It hurts to wreck the original diaphragms, but it has to be done.
2/19/25
The last of the gluing and taping supplies I ordered arrived today.
I took one of the stators out of one of the bass drivers today to assess the condition of it and the grid and to figure out how I want to proceed with regluing it. Taking it off the grid required desoldering two metal connection clips.
Once I had it out I could see that the copper side of the stator, the side that gets glued to the grid, is covered with some sort of clear plastic coating. There are a couple small spots along the edges where the coating seems to have failed and the copper looks corroded.
I gently scraped the larger bits of glue off the stator, being very careful not to damage the clear coating. I also scraped the glue off the grid. Then I set the stator back into the grid to see how it sits. The three screw posts at the center of the grid protrude loosely through holes in the stator, and it looks sufficient to align the stator within the grid.
The stator is pretty flexible and has a bit of a curve to it, so it will have to be weighted down to ensure that it glues onto the grid as flat as possible. The stator requires very little force to flatten it on the grid, so I cut three pieces of the 1"x1" foam weatherseal to the width of the stator and stuck it to a plywood board. The weatherseal foam is very soft so it won't damage the stator. I'll put a little weight on the board when gluing to ensure the entire stator is flattened against the grid.
Update 2/22/25
I tested some clear polyurethane Gorilla Glue on a couple small parts to see if it expands or foams when it cures. Per the instructions for the glue, I wiped one glued surface with a damp paper towel (apparently the glue needs some moisture to set properly), then applied the glue and let it set for a few hours. It did not expand or foam at all, and set up just fine, so now it was time to try it on one of the stators.
I transferred some of the glue from its bottle into a 5cc gluing syringe with an 18 gauge needle. Then I set the grid down on the table, wiped a few of the vertical ribs with a foam paintbrush that had been dipped in distilled water and squeezed so it's just damp, and applied thin beads of glue to each of the damp vertical ribs. After applying glue to a few ribs, I wiped a few more with the damp brush and applied more glue until all the vertical ribs had thin beads of glue on them. Then I set the stator down on the glued grid, first setting the center hole over the post, then adjusted it so the other two holes aligned with their posts, and finally set the whole thing down on the grid. Next I covered the surface of the stator with a piece of saran wrap in case the glue wicks through the stator - I don't want it sticking to the weatherseal on the clamping tool. Finally, I put the clamping tool and some weight on top to ensure the stator was pushed flat on the grid.
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| I dampened and applied glue to the vertical ribs on the grid, placed the stator, covered with saran wrap, then placed the clamping tool and some weight on it to hold the stator flat against the grid. |
If I continue to use this clamping tool, I'll only be able to glue one stator at a time. The glue sets in 2 hours, and needs 24 hours for full set, so it will take a couple days to finish these grids/stators. I'll work out the technique and get started on the grids with the diaphragms next.
Update 2/2325
The first stator is reglued and it looks like a complete success. There are a few areas where the glue was wicked up to the surface of the stator, but a quick, gentle scraping removed anything that was sticking up over the surface of the cloth resonance damper.
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| Reglued stator. The green arrows point to some areas where there was excess glue that wicked up to this side of the PCB. A quick, gentle pass with the scraper took off the stuff that wasn't laying flat. |
I prepared the next one, glued and clamped it. Today I added two more steps to the process. I removed most of the solder from the stator PCB, and wiped the glue side of the stator with distilled water before the gluing operation.
I clamped a piece of aluminum to the stator against the cloth resonance damper to dissipate heat from the iron so it wouldn't melt the cloth. I set the iron for 700F- just hot enough to melt the solder, and desoldered with a solder sucker and wick.
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| Aluminum clamped to the stator for desoldering. You have to remove the solder so the stator will sit down flat in the grid. The aluminum acts as a heatsink to protect the cloth that's glued to the bottom of the stator. |
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| Stator with flux from desoldering wick. That needs to be cleaned up. |
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| This is what it should look like after you clean the flux off by wiping with a towel soaked in IPA. |
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| Applying glue to the grid. I use clear polyurethane Gorilla Glue and wipe the grid with distilled water just prior to applying the glue. Then I wipe the stator with water before setting it down on the grid/glue. The glue needs the water to set properly, so don't skip this step. |
Here's the sequence for gluing stators that do not have diaphragms attached:
1) Carefully peel the stator away from the grid, and unsolder the metal clips that hold it on the grid. Now you have the two pieces, the grid and the stator, separated.
2) Scrape the old glue off the grid, vacuum up the crumbs.
2.5) Clean some of the solder off the clips on the grid.
3) Carefully scrape the old glue off the stator and vacuum up the crumbs.
4) Clamp aluminum to the stator and remove solder with a solder sucker and/or wick.
4.5) Clean up solder flux on the stator board by wiping with IPA
5) Wipe a few of the vertical ribs on the grid with distilled water, apply glue using a syringe, work your way across the entire driver with water, then glue.
6) Wipe the stator with distilled water, then place it in the grid making sure to put the solder pads on the stator against the metal clips to which they will be soldered.
7) Place the saran wrap on the stator/grid, then the clamping tool, then add the weights on top of the tool.
8) Wait a few hours and check the work- carefully scrape the stator as needed to remove any excess glue from the cloth side of the stator. Vacuum up crumbs.
9) Clamp on the aluminum and resolder the clips from the grid to the stator board.
The first 7 steps take about 15-30 minutes. The last two take no more than 5 minutes.
Update 2/24/25
Today I finished regluing the stators on the non diaphragm sides of the drivers. The first two that were done have had >12 hours for the glue to harden and are rock solid. Today I will work out the procedure for regluing the other stators, hopefully without having to replace the original diaphragms.
I ordered more of the 18 gauge gluing needles. I have used one 5 cc syringe for this so far, but gluing each half of each driver requires a new needle. Regluing all four drivers will require 8 needles, or 16 for a pair of speakers.
Update 2/26/26
A couple of the driver's stators are mostly separated from the grids and that's going to make regluing them very difficult without removing the diaphragms. There's no good/safe way to grab the stator, in many places at once, through the grid, without risking breaking the stators and/or the diaphragms. If I put some weight on the center of the diaphragm to push the underlying stator against the grid, I risk excess glue sticking to the diaphragm. I'm going to have to remove the diaphragms, reglue the stators like the one's described above, then put on new diaphragms.
I have a bunch of 6 um film I could use for the diaphragms, but the original stuff in the speakers was 3.5 um. I would rather have it be a little light than heavy, so I ordered 40m x 620mm x 3 um Mylar via ebay. That will leave plenty of extra material to rebuild these as well as drivers from my old pair of ESL-63s. While I'm waiting for delivery I'll keep looking at the drivers. Maybe I'll get a new idea about repairing them without replacing the diaphragms.
Update 2/27/25
I've been thinking about how to place new diaphragms. There are two important things to consider, both of which relate to the tension applied to the film. First is the resonance of the panels, though I'm not sure how important it is to the final sound of the speakers, and the second is that the tension be sufficient to prevent the diaphragm from sticking to the stators when high voltage bias is applied.
I don't currently have any way to measure the resonance other than to thump a diaphragm with my finger and listen to it, and my stretcher table is not set up so that I can excite the resonance while I'm stretching the diaphragm. However, I have drivers with intact diaphragms, and that means I should be able to determine what % of stretch is applied.
What I'm thinking is that I'll make a couple marks 500 mm apart on one of the intact diaphragms then cut the diaphragm free of the driver and lay it out on a flat surface and measure the spacing between the marks with the tension released. Let's say the marks are 495 mm apart. I can then put a couple marks 495 mm apart on the stretcher table and use them to mark the untensioned new film, then stretch the film until the marks are 500 mm apart. That should get me the same amount of stretch, the same resonance, and should ensure that the diaphragm won't stick to the stators when HV bias is applied.
It may be that very small, indistinguishable amounts of stretch cause the resonance to vary widely. I'll be trying some experiments to check it while I wait for the 3 um film to arrive.
I am also considering some modifications to the stretcher table that would allow me to check the diaphragm resonance under tension.
In the past I have used contact cement to glue the diaphragms to the grids. The stuff I have used (4693H) is stronger than the film, and the diaphragms I glued about 30 years ago are still holding. Today I tried an experiment with the clear Gorilla Glue I used on the stators to see if it can be used. I took a piece of my 6 um film, dampened it with distilled water, applied a drop of gorilla glue, and folded it over. I let it set for >4 hours and it peeled right off the film. Nope. Don't use Gorilla Glue to glue the diaphragms.
I checked my old can of Licron Crystal antistatic spray and found that over the years it had leaked and was empty, so I ordered a new can today. The data sheet is here. This stuff makes coating the diaphragms very fast and easy, and it sticks to the polyester for a long time. I checked the resistivity of a couple of the old driver's that I had rebuilt about 30 years ago and they are still fine.
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| Original diaphragm (on my new speakers) resistivity reads 10^7 Ohms/square |
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| One of the diaphragms I put on a driver about 30 years ago and coated with Licron. Resistivity is also 10^7 Ohms/square. The 4693H contact cement I used to hold the diaphragm on the grid almost 30 years ago is still holding fast. |
One difference between the old and new speakers is that the new stators have some clear coating on the copper sides that get glued to the grids. The old drivers didn't have any coatings applied. There's no way to know how long the Gorilla Glue will hold the new drivers' stators. I guess I'm going to find out. I don't remember having to reglue the stators 30 years ago, so I think those drivers have original glue holding them and they seem to be solid. Maybe the reason the newer ones are all letting go is because of that clear coating they put on the copper/glue side of the stators.
I'll need to make a stencil to block off areas of the diaphragms that I don't want to have coated with the Licron when I spray it. IRIC, I used a paper stencil and some circles cut from post-it notes. I think a stencil made from sheet plastic will be better this time.
Update 3/1/25
I drew the film in CAD, and marked out the area covered by the high resistivity coating, thinking I would use the drawing to make a stencil for spraying the coating on new diaphragms. Then it occurred to me that I could simply 3D print a couple pieces that will fit on the ends of the driver to block out the areas that don't get the coating.
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| This is the area (gray) of the diaphragm that needs to be coated. The left and right edges are left uncoated to reduce leakage current due to proximity with the metal frame that the drivers are mounted on. The center circles also need to be blocked out because of the metal screws that go through the holes. |
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| Crudely printed mask that fits over the end of the driver to prevent the sprayed-on Licron coating from going there. I'll make two of these and 3 small circular pieces to mask off the center holes, too. |
When it's time to spray the coating on new diaphragms, I'll mask off the long sides of the driver with masking tape, place the two end-covers and the three hole covers, spray, then remove the plastic pieces and the tape.
update 3/2/25
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| End mask to block conductive coating on new diaphragms. Dimensions in mm. If you make holes in the specified locations you can use screws to align the mask with the driver, otherwise, just put some masking tape on the edges to hold it in place while you spray with Licron. |
I have ordered a proper 600 mm steel ruler to measure the spacing between marks I'm going to make on the existing diaphragms before I cut them free of the grids. Once the ruler arrives, I'll mark all four of the original diaphragms, cut them free, and measure the spacing of the marks. Then I can mark the diaphragm stretcher with the start and finish marks, and reglue the stators on those sides of the drivers in preparation for putting on new diaphragms.
Update 3/4/25
The 3 um film and the Licron Crystal are both supposed to arrive today.
The process of removing the old tape and its residue was so messy, that instead of cleaning up now, I think I'm going to open the other speaker up and get it ready for diaphragm replacement, then do the clean-up, and replace all the diaphragms in one go. I'm expecting the process to be the same as detailed above, but if I run into any interesting differences between the speakers, I'll post updates with photos here.
I designed a printable mask for the circular holes in the diaphragms yesterday and printed three of them today. The STL file is here. They are designed to use M3 screws that will go into the screw holes in the plastic grid to ensure they will be aligned with the holes in the diaphragm.
The diaphragm replacement procedure will be:
1) put reference marks on the original diaphragm spaced 500 mm apart.
2) remove the diaphragm in one piece, lay it out flat and measure the spacing between the reference marks (it will be less than 500 mm)
3) put reference marks matching the spacing of those on the diaphragm on the stretcher table.
4) clean old diaphragm adhesive off the grid using acetone and a scraper
4.2) recement the stator using the procedure detailed above
5) put new 3 um film on the stretcher table, smooth it out, and inflate the tube just enough to pull out the wrinkles.
6) trace the reference marks from the old diaphragm onto the film
7) inflate the tube until the reference marks on the film are 500 mm apart
8) apply 4693H glue to the diaphragm and grid and let it set for XX minutes
9) put the grid down on the diaphragm, apply weight or clamps, and let it set for XX.
10) Cut the diaphragm free of the stretcher table and turn the grid over.
11) using a soldering iron set to a low temperature, melt holes about 10 mm diameter in the diaphragm over the screw holes in the grid
12) put masking tape on the long sides of the grid.
13) place masks over the ends and center holes of the diaphragm
14) spray a light coating of Licron Crystal, remove the masks, and let it sit for XX.
15) test resistivity of the coating- it should be at least 10^7 Ohms/square
16) assemble the driver and test it
Oh boy! The new diaphragm film and my 600 mm ruler have arrived.
I decided to check the stretch on one diaphragm by making marks 500 mm apart on it with a fine point permanent marker. Then I cut the diaphragm free of the grid it was glued to and measured the spacing between the marks- about 496.5 mm. So the film needs to stretch about 3.5 mm on the long dimension. I will also check it on the other 3 diaphragms for this speaker as I prep them for regluing their stators.
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I made marks 500 mm apart on the diaphragm before I cut it away from the grid. After I cut it free, I laid it out and measured the new, closer spacing of the marks- 496.5 mm.
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| The new spacing of the marks- the relaxed film marks are 496.5 mm apart. |
I will be working on the stators for the next couple days, then put on new diaphragms.
Here are some photos of my stretcher table. It is 660 x 270 mm, and I use a 20"x1.35 bicycle tire tube on it. The top is 1" thick MDF, the lip is made from 1/2" x 1.5" wood strip, and I put a couple smooth floor tiles on it to lift the film and grid a bit to make it easier to cut the film free of the stretcher (best done with a hot knife).
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| Underside of the stretcher table made specifically for ESL-63 drivers. Note the legs are set inside allowing room to install double stick tape and to wrap the film on the table. |
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| End view of the table. Notice the corners and edges are all rounded to prevent tearing the film when it's under tension. |
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| Top view of the table. I have added smooth floor tiles cut to match the outer dimensions of the driver grids. I also added lines with a permanent marker showing the area to put adhesive and the 500 mm marks for tension reference. Note- I drilled a small hole at the center to allow air trapped under the film to escape when the film is being tensioned. |
Update 3/5/25
Today I started cleaning up one of the grids that had the diaphragm glued to it. I started by desoldering the clips that hold the stator on the grid, as described previously. Once the stator was loose, I cleaned off the solder flux, then started working on cleaning up the grid with a scraper. I scraped the vertical ribs, then went to work on the perimeter of the grid. When you take a diaphragm off its grid, parts of it will remain stuck to the perimeter. You have to clean all that, and the glue, off the grid perimeter.
I found that the old glue didn't really bond well with the diaphragm. It peels off the glue very easily. I guess Quad was relying on the shear strength of the glue bond, not the peel strength:
The 4693H glue that I will use to replace the diaphragms actually bonds to the polyester film and will not peel or shear off easily. I will post a video of that in the near future. Some people think that using double sided tape will work for this job. Not true! Tape has soft adhesive that will move toward the center of the driver due to the tension on the diaphragm. That means the diaphragm will lose tension and you'll have gooey adhesive pulled into the air space between the grid and the diaphragm. It will work for a few hours or days, then the diaphragm will get so loose that it will stick to one of the stators. Don't use tape for the diaphragms.
Other people think they can heat shrink the film, and yes, it will shrink when heated, but it won't give sufficient tension and from what I've seen online, it "relaxes" after a while and will lose tension.
The grid perimeters are slightly concave, so you can't really clean them off with just a scraper. The first step in cleanup is to peel off the remains of the old diaphragm. Once that's done, you remove the glue by wiping with a paper towel or cloth wetted with acetone. The glue will dissolve and the plastic appears to be unharmed by it. Fold the cloth over frequently when wiping with acetone.
It might be possible to clean the old glue off the stators by wiping with acetone, but I am afraid to try it because the acetone may attack the clear coating on glue side of the stators. Maybe I'll try an experiment along the edge of one stator to see how acetone affects the coating.
I tried using acetone along the edge of one of the stators- no problems! It didn't damage the clear coating on the stator and made it possible to get more of the old glue residue off. I cleaned the remaining stators with acetone before regluing them. A little of the old glue remains inside the holes in the stator. That's OK, it's not going anywhere.
Once the grid is clean, you can reglue and solder the stator using the process described previously.
I'll be working on the remaining three grids/diaphragms later today, and regluing their stators. It will likely be a week or so before I install new diaphragms as I am going to get the other speaker caught up to this one before I start installing new diaphragms.
Update 3/6/25
Today I removed the diaphragms from the other 3 drivers, measuring the stretch of each before cutting it free of the grid, then prepped them for regluing the stators and for replacing the diaphragms.
The first measurement I made on 3/4/25 was 3.5 mm. The 3 diaphragms I measured today were all 2.5 mm. It's a hard measurement to make consistently. The film is very loose, so I tape it down when I make the measurement, and try not to stretch it- just pull it enough to remove wrinkles.
I've seen videos of people measuring the driver resonance using calibrated microphones and audio sweep/analysis software, neither of which I have, but I had an idea for another method. The tight diaphragm sounds like a drum if you tap it with your finger. Drums are just stretched skins in a rigid frame, just like the ESL diaphragms. I should be able to measure the resonance by looking at the waveform the diaphragm makes when it is tapped.
I made a recording, using my Sony PCM-10 digital recorder, of me tapping a diaphragm with my finger. When I do that, the diaphragm makes a sound like a drum, at the diaphragm's resonant frequency. Next I opened the recording in Audacity and zoomed in on one of the "taps" and measured the waveform. The resonant frequency should be equal to the number of cycles of the waveform divided by the time they take:
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| Audacity shows the many finger taps on the diaphragm. From these I selected one that had large amplitude without hitting the amplitude limit of the file/recorder. Note that Audacity shows a time measurement at the bottom of image. |
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| Here is a zoomed selection of one of the "taps" clearly showing the waveform. The even spacing of the peaks and troughs is the main diaphragm resonance. |
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| Here is a selection that starts and ends on peaks of the waveform. I skipped the initial stuff that has my finger in contact with the diaphragm and went for the relatively clean decay after the tap is over. The time duration of that interval is 12.270-12.107=0.163 seconds. There are 16 cycles in that interval, so the resonant frequency is 16 cycles / 0.163 seconds = 98 Hz. |
I zoomed into a few more of the recorded taps and got the same 98 Hz resonance. If you want to look at this yourself, you can download the .wav file from my recorder here. Yes, I know, Audacity can plot the spectrum using FFT, but I don't trust the reliability of it with so few data points.
The waveform isn't a perfect sine wave because there are multiple things going on at once. The primary resonance is probably from the width of the diaphragm, but there will be another resonance at a higher frequency based on the vertical dimension of the driver. Then there's background noise, etc. adding in to the mix.
I only thought of this test when I was getting ready to remove the 4th diaphragm, so I only have recordings for that one. When I take apart the other speaker, I will test each of the drivers this way to see how consistent that are from one driver to another. I will check the new diaphragms this way after I install them.
Now, back to prep for, and regluing stators...
I found that the remnants of the diaphragm peels off the grids easily, so the first step is to just do that, then I unsolder the clips and gently break the stators free of the old glue.
Next I desoldered the stators, cleaned off the flux with IPA, then carefully scraped the larger bits of old glue off, and then wiped the remaining glue off with acetone and set them aside.
The grids are the same as those previously prepped for stator regluing, except that there's a lot of glue on the perimeter to hold the diaphragm. I scraped off as much as possible (the surface isn't flat, so you can get it all with the scraper), then cleaned off the remaining perimeter glue with acetone. Finally, I scraped the vertical ribs clean.
Then I vacuumed up all the crumbs and reglued the stators one by one, as was done previously. First, I wiped the ribs with water, placed the glue using a syringe, and then I wiped the stator with water just before I set it down on the glued ribs. Once the glue was set, I resoldered the clips.
Next up: take the other speaker apart, clean up the old tapes and replace them.
3/9/25
I got busy doing some other things so I didn't have much time to work on the speakers today, but I did find time to design and print the missing feet for the speakers. I opted for a design that consists of a PETG holder that spans the bottom of the electronics enclosure from front to back, and accepts TPU inserts. The inserts can be flat or can be made to tilt the speakers back at any specific angle. For now I printed flat inserts, but I may make a set or two of angled inserts once the speakers are playing music again.
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| Universal foot- each speaker needs 2 of these. They hold inserts that can be flat or made to any desired angle to tilt the speakers. |
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Flat TPU inserts in place. Yeah, I know, the color...
I didn't have any black TPU to print these. |
You can download the STL files for the universal foot (the black piece) here, and the flat foot insert here.
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