Mr. Weather

It is cold and rainy here in Houston. Perfect weather to stay inside. I started on the crossover work. I will use standard NPE capacitors all around, with the addition of 0.01 uF poly capacitors in parallel to the 4, 6, 24, and 80 uF capacitors, with the goal of revealing a bit more sound detail without affecting performance. Below I have the white 0.01 uF CornellDublier 940C caps glued and soldered to the NPE caps. I got the 940C from Mouser and the NPE caps from Madisound and Parts Express. I also ordered a new set of Pomona "minigrabber" test clips for my Fluke 115 meter in hopes of getting more accurate capacitance readings, especially from the old caps. So we'll see if that makes any difference. I recently successfully replaced all of the capacitors, inductors, and resistors in a pair of Original Large Advent (OLA) cabinets without removing the crossover boards from the cabinets. That worked well enough but those crossover boards are less cluttered than the AR-90 ones. However that gave me some confidence that I can replace the AR capactitors with the boards in place without too much grief. I am using my son's Haiko soldering station which is quick and powerful. The main hurdle is my old eyes.

On the original grill cloth project: I was able to wash the original grill cloth, and oh man the water was dirty, a grey-brown color. Yuck. I moved each cloth to the wooden frame where it was washed and dried. This avoided any shrinking. However, ultimately the cloth had enough damage from 50 years that I replaced it. I was unable to remove the large stains on the cloth by soaking in water with detergent, light brushing, and using stain remover. The one apparent best source for this cloth, Dorr Mill, was out of stock. So I used a less expensive and lighter colored cloth from a different source. I used the "Speaker Fabric Grille Cloth for AR Advent KLH Kloss Dynaco Restoration Repair" from this ebay listing and this seller. I ended up using 1/4" staples with 2 layers of corrugated cardboard on top of the fabric to precent putting the staples through the front of the board. I did not replace the black backing cloth. The speakers look great with new grills and badges. Just need one more tweeter.

Great news: I replaced the capacitors, resistors, and the 2 small inductors on both crossovers and this fixed the problem. The one speaker with an original tweeter sounds great. I still need to source a replacement tweeter for the other speaker.

Thanks! It's been a fun but slow project. I ordered another kit of epoxy and will use that to get the base totally flat and to attach on the new plywood and oak bottom piece, shown below. Still waiting on the walnut veneer. That's the main hold up right now.

Work is still moving along: I epoxied the bottom of the speaker that had damage to the MDF. This worked well although I could have used a second box of epoxy. Having done this once, I got a great appreciation for the process and I could do it again better on another pair of these. However this is a very good solution for the damaged MDF. The black backs of both speakers have been sanded bare and repainted in a matching black. I cut a new bottom base for the cabinet that had the MDF damage. Instead of using 3/8" MDF or particle board, I used 1/2" plywood. Additionally, I added a 1/4" layer of oak around the perimeter of this new piece. I will add the same oak boards to the bottom of the other cabinet and this should help prolong the original MDF there. The oak will provide a strong surface for mouting metal feet or felt or whatever may be needed in the future. No photos of this yet. I was able to remove the plastic "poly grill guide" sockets from the cabinet sides using a die grinder to remove the plastic material from the inside of each socket. This weakened them and allowed me to pry them out without pulling up the veneer. This enabled me to sand the veneer surface completely. I got replacement grill guides from Parts Express to ensure these will work before removing the old ones. I'm still waiting on the walnut veneer. Should be here in 2 or 3 days. Today I will ge the new footer boards installed and get some photos.

I am still working on the OLA set that I posted about in this thread. One of of the cabinets is missing its original tweeter. Should I look for a matching red fried egg tweeter, or should I get a pair of some other Advent tweeter variant? This is what I'm starting with:

I got the replacement capacitors inststalled but the tweeter output on both speakers is very low. On the speaker with the original tweeter, I can switch the crossover to 'extend' and get louder output, but the tweeter's volume is a fraction of where it should be. The other speaker with the Realstic tweeter performs simialrly. If I connect either tweeter directly to the speaker wire, its output is much louder. So I'm thinking something on both crossovers is bad. What's the most likely culprit? I found these 0.8mH air core indcutors on parts express for under $5 each. According to this thread, air core inductors should be adequate. I can replace the resistors but those seem unlikely to wear out.

My plan on the grill cloth is to staple it to a temporary frame, below. This will hopefully keep the cloth from shrinking during cleaning. The frame is cedar becase that was the first board I pulled off the lumber stack. The joints are crude mortise and tennon with gorilla glue. Should be enough to withstand some soaking in water. Note the shop cat enjoying the warm afternoon sun. As far as actually washing the cloth, I asked my wife who is a laundry wiz. She said to soak in cold water with laundry detergent and avoid any stain removing sprays at first as those might cause lighter spots since the cloth is probably several shades darker than it was originally. I will have to get some really shallow staples before reattaching the cloth back to the original frame.

Yes, good point. The single original gasket is very thin, less than 1/16". For the woofer reinstall, I used Parts Express 1/8" speaker gasketing tape thatI've used in the past. It did make a good seal and the woofer cone does respond slowly after being pushed in. Of course on the other cabinet in this pair, with the Realistic tweeter, the woofer cone pops right out becauase there is a large air leak around the tweeter as you can see below.

I realize this post is at least a couple of years old, but claimed "AR300" is actuually an ARS 300 powered subwoofer. Crutchfield used to sell them: https://www.crutchfield.com/S-KPexE7TsbdM/p_058S300B/Acoustic-Research-ARS300.html The AR15 turned up in one Ebay listing that doesn't look to have gone anywhere yet.

One final note based on my testing: 4 coats of 'natural' Danish oil with a coat of Odie's Oil on top is fantastic with a deep, rich, super smooth finish but moves the finish into gloss territory which you said you wanted to avoid. This is a test strip I did last week with one coat of each product. The darkness difference is minimal in real life, the camera lighting makes it hard to show the real look in a single photo. Anyhow, something to consider if you want to test on other wood. I got these small strips on Ebay for about $6 each.

I did a test with non-tinted Danish oil on new walnut and the results are good. I plan to use it on my AR-90s which have been sanded and are awaiting other parts and veneer repair. Danish oil is typically a blend of equal parts of a solvent (like turpentine), a varnish (like polyurethane), and an oil like linseed oil. However any particular product will probably vary and may not reveal its specific contents. Danish oil is somewhat thin and soaks into the wood quickly. You can apply a second application after 15 minutes or so, wipe off the excess then give it a day to dry. Then do 3 more applications, one per day. You could sand with 400 at some point and use XXXX steel wool before the last application. Then give it a few days to cure. I did not get any noticable sheen until after 4 coats and polishing with a cloth. That gave me a really pleasing, natural looking satin to semi-gloss finish that really makes the natural wood come alive without being showy. I also experiemented with Odie's Oil, which has a lot of fans and it works well too. It is a mix of oils and waxes and is like cold honey: really thick. You wipe it on, wait 15 minutes to a day, and rub it off. It gave me a similar finish to Danish oil but with less shine. A varnish or Danish oil will give you a harder, more durable finish than an oil/wax finish and that may be desireable. Consider getting some test strips of wood and doing a test with a few products to see what might work.

The woofer surrounds are done. It's amazing how the old adhesive on these things is diffifult to remove, even with acetone. I also tried to remove the adhesive from the old failed rear gasket but it was just as stubborn to remove with acetone. I was able to remove 90% of it. For the blown out woofer mounting hole, I used a #10-24 T-nut with 2 of the prongs removed. I put a small amount of epoxy glue to help hold it in place just in case. The screw is 1.5" too long but works OK. Once the replacment capacitors are in I'll be able to listen to these things and see where the tweeters are.

I pulled out the woofers this morning to start re-foaming them. The first thing I noticed is that one of them had what may be the original gasket between the woofer frame and cabinet, but also had an aftermarket thick foam gasket that had been installed wrong. The second woofer had the same botched gasket install. The posiotioning of the new gaskets made it seem like whoever installed them did not know what they were supposed to do or how they needed to be located to make a seal. Anyhow, those are gone and the original single thin gasket from one woofer is actually intact. There is also a remnant of an old white-colred sealer or glue around the woofer holes. PResumably this needs to be sanded off to ensure a better seal. Finally, one of the screw holes is blown out. The masonite crumbled in the area. The only way I know to work around this is to install a T nut with a machine screw in place of the wood screw. This would ensure a strong bond. I can't see that the particle board can be repaired well enough to hold the large wood screws that are in this thing. Finally, I found it intersting that the woofer wires were soldered to the woofer! I loaded the joints with flux and was able to de-solder the wires fairly easily.

I like that idea but I'm worried that the masonite absorb water and fall apart, bulge, or become distorted. This may be more work, but I could make temporary frames, transfer the grill cloth to those, wash the fabric on the temp frames, let it all dry, and then re-attach the fabric back to the original frames. I love the idea to try to clean the original fabric because getting the right fabric is expensive and I'd love to know that these have the original fabric.

I started sanding the second speaker last night. It had some gouges in the top that required deeper sanding but fortunately I did not sand through the veneer. This second speaker had drips of grey paint on the back and brushed-on black paint over those, so I ended up sanding the entire back. So the second speaker has been sanded entirely except the front black. Also, great news, the base of the second speaker has far less damage than the first speaker. The base is pretty much entirely entact, and now I can see that the bulging button of the first speaker is just water damaged MDF. The second speaker does not have this problem. The second speaker does have some damage at the corners but this is minor. I didn't get an 'after' photo of the second speaker but overall it sanded well. I am still waiting for the epoxy, capacitors, and other parts to arrive for this project. On the first speaker, I need to sand the entire back. The test spray of black paint was good but all of the original black paint will need to be removed from the back to ensure an even looking new black spray. This is not surprising as a paint job is only as good as the surface that's being painted. Right now I have 2 hurdles: First, the plastic grill peg sockets/holes are in the way of complete sanding on the sides. Removing the sockets by pulling them out damages the veneer, however I can use a die grinder to remove their plastic to the point where they should come out without a fight. However before I do this, I want to make sure that the new plastic sockets on order will fit correctly. So I need to wait for those to arrive. Second, the walnut veneer is damaged on the first speaker near the bottom. A thorough repair job should really include fixing that. To fix veneer, the damaged and missing veneer can be filled in with epoxy and sanded. This will result in a non-matching spot. The better method is to cut out the damage veneer and replace it with new veneer. This results in a less obvious repair and shows an attempt at a correct repair. Either method, done properly, should help stop the veneer from continuing to peel off. I ordered some walnut veneer to make a proper repair. My test panel with 4 coats of Danish Oil on walnut wood looks great. 4 coats applied over 4 days gives the most sheen and depth to the wood. I polished it with XXXX steel wool after day 3, and then polished it with a clean cloth after day 4. On the Advent forum, I have a thread going for a local set I found that needs some love. So I'm re-foaming those today. The worst things I've found so far are the incorrect use of gaskets between the speakers and baffle board, and a replacement tweeter wired right to the woofer's positive terminal.

Great information. Thanks very much. I will remove the grille cloth staples and try to gently clean the cloth. If it doesn't work, or falls apart, I'll have to go with new. Yep, not surprised to year that. Will replace for sure. Starting off small, I mixed up some Murphy's Oil Soap and water and scrubbed the cainbets. The resulting soap-water turned a very dark brown-grey. It was so dirty I mixed a second clean batch for the second speaker. I did not notice a huge difference while cleaning them, but the two cabinets do now have a much more identical look when sitting together. That and the resulting nasty colored water seem to indicate that the work was successful. I don't like using water on wood, so tried to mimimze the exposure and I dried them with a dry rag while I was scrubbing with the other. Then I let them air dry under a fan just in case. I will get the capacitors ordered and get the wooder surrounds installed when I have a spare hour or two. I am in the middle of a project to restore a pair of Acoustic Research speakers and that's taking up much of my free time. I have installed woofer surrounds on two other sets of speakers so hopefully this Advent project will be successful. Looks like I need to line up a tweeter, although I think I will get the new capacitors installed first so I can listen to this original tweeter and make sure it's not a problem.

Great news, the offending black was sanded off gracefully without damage to the veneer. With a Bosch random orbit, variable speed sander, I started with 220 grit but switched to 150 grit for the bulk of the paint removal. Then I made a pass with 220 to remove the smallest remaining bits of paint. I sanded all of the sides, including the factory black area. I also sanded the large scratches on the back of the cabinet and test painted a corner with black to see if that's going to work, of if I need to sand the whole back before painting it black. The initial result is that the scratches are pretty deep so I may end up needing to deep sand the whole rear panel. I also worked on the base: The base did not have screws, but had small finshing nails. I was able to remove the original "circle cutout" base (what is left of it) but I'm confused about what was left behind. You can see the odd round bulge on the bottom. So what's my move here? shore up the edges with wood blocks and flood the whole base with epoxy, including the round bulging part? Then glue on a new solid oak base? That's what I'm thinking. It's now occuring to me that the circle is bulging because it was wet and it was not originally like that. Today I only did one speaker. The other one is still inside waiting to be sanded. It is slow work, even with the sander doing the hard part. I also shot some video of the work today and will throw together a video to document this project after all of the work is done.

I picked up these Large Advents for $60 locally as a project. First, I need help in idenfying them as being OLA or NLA or a combination of the two. Some key points: They are the older style (non-bullnose) cabinets Newer frame woofers (no masonite). One has what looks a serial number inside: A 50766. If that is a serial number, at least this unit would appear to be an Original Large Advent if my research is right. These look to be a mismatched pair with sightly different colored masonite grill frames and different insulation inside (one is pink, one is yellow) One has a replacemt vintage Radio Shack tweeter that is wired right off the woofer's positive lead which means it probably never performed as intended. The remaining red fried egg tweeter's date is just about impossible to read, AND its grill is slightly pushed in, possibly touching the cone. Not sure if this is visible in the photo. I will pull it back out slightly. Second, what are the best potential paths forward? Clearly the woofers need new surrounds. At least I need to get a used red fried edd tweeter, but maybe the better play is to replace both tweeters with a newer model from a NLA or similar? I assume the fiberglass insulation is Ok to leave there? No need to replace with polyfill? Assume the capacitors should be replaced. My capacitor meter has been flakey so I don't trust it to give me an accurate reading. Try to remove and gently wash the grill cloth, or just replace it. The cabinets are in great shape overall, and can probably be carefully cleaned and then polished with one of the usual 'natural' wax and oil-based products. Add replacement badges Your thoughts are welcome. I have to keep these photos small in resolution to avoid blowing my storage quota, so I apologize for the small resolution of these.

Makes perfect sense. Thanks. Ultimately, in keeping with the original design of the crossover, I'm going to stick with regular NPE capacitors. I was able to source exact or near exact values from Parts Express and Madisound. I don't think I'll have to remove any of the crossover boards. The hardest capacitor to reach is the 6 uF unit on the top of the rear board but I can access it through the woofer hole on the left side. The Z-Poxy is on order but will take a week to arrive. I have another test strip of walnut going where I've added an additional coat of Danish oil every 24 hours. Probably 3 coats is plenty but the test panel has 4 squares so we'll see if there is any benefit to 4 coats. The weather will be dry, sunny, and slightly cool Sunday so I may haul the cabinets outside and see how the veneer stands up to some careful sanding. I also have to deal with the bottom panels and the screws with no heads. Ideally I can remove the MFD around the screws and then use a vice grip to unscrew them. I have other more forceful methods but will start small. In a non-related topic, I pulled the trigger on a local pair of "parts only" The Advent Loudspeakers for $60. I will post a thread over on the Advent forum.

Can the screws in the tweeter below be removed safely without risking the tweeter? They need rust removal and possibly painting, but I don't want to risk the driver.

Yep, that seems to be a workable combination. Those 2 values seem to be fairly common. Good call. I checked against a known new capacitor and got nothing. Based on that I'm inclned to think the Fluke 115 is flakey. Either way, the capacitors are old and should probably be replaced. My meter doesn't have settings for frequency as far as I know. It is auto ranging for farads, but I couldn't get readings in either auto or manual modes with the known good test capacitor or the AR90 capacitors that gave no reading. I found this place: https://www.madisoundspeakerstore.com/solen-capacitors/ They have a great selection of Solen "metallized film, polypropylene, non-polar" capacitors. But holy cow, the full array is going to cost $214 per speaker, plus shipping Maybe they will last for a long, long, long time. Friday I should be able to pull the drivers from the other AR90. I made some wooden and cardboard panels to fill in the driver holes to help keep dust and debris from getting inside the cabinets. Then I can get them outside and get the bottom MDF panels off and hopefully work out a plan to restore the bottoms. I like the epoxy idea of bar clamps and wood blocks to shore up the sides while the epoxy cures. I need to come up with some way to protect the acoustic blankets and front of the cabinets, without getting in the way of the sides of the cabinet. Probably painter's tape with a custom made shallow cardboard tray to cover the blanket.

I measured the capacitors in the first speaker using a Fluke 115 multimeter. The values are shown in an image below. These are way out of spec. Three of them did not yield a capacitance measurement but they did pass a continuity test. Normally I would buy replacements at parts-express.com, but they do not offer a 350 uF. Does anyone have a reccomendation for something other than parts-express.com? The 80 uF units are $42 each. Also, some of the capacitors have two terminals on top but the items at parts-express are all axial with a wire on each end. Not sure if this matters or not.

I started disassemly. I am labeling all of the parts with the last 3 digits of the serial number of the speaker they came from. (521 and 518). Probably this makes no difference but couldn't hurt. The drivers all have the white/pink "Made in USA" part numbers on them. One indicates it is a "service replacement unit". The drivers all appear to be stamped with "SFT 8" in black ink. One woofer screw is wrong: too long, and one size too small. The original gaskets on the LMR and tweeters appear to be intact. The woofers will need new gaskets or gasket tape which I have. The brace above the woofers is stamped with "56181 10" Is this a date code? October 1981? The bottom screws have no heads. Probably cut of sheared off. When I get the thing outside and preppred and sealed up, I'll try to pry that off. The only capacitors I could identify by name are Callins. To remove the rear crossover board (the one with the external connections/controls), I assume I pull out the staples that holds it in? A few photos:

Good information. I should stop asking qurstions until after I've disassembled things. I can see how the circular base would work better on carpet by creating more pressure over a smaller area compared to a piece without the cutout. Is there a single library of technical and related information for restoring this model? Some consolidated resource that covers the well known hurdles with restoring these, either here or somewhere else on the Internet? It would have data like capactor sources, important bits from the owner's manual such as the reccomended polishes for the walnut veneer, other part numbers and sources, repairing common problems like a damaged base, etc. It would help folks like me from reinventing the wheel each time