Upcoming AR3a project

[ra.ra]

Another terrific foto from JKent - - - but unless I am missing something, I think you meant to say your replacement drivers are rear-wired. To me, this is a great-looking update of a very old speaker. Nice work!

Excellent comments from RoyC as well - - I think I read here somewhere about the early aluminum leads, and I would hazard to guess that these would present an unsurmountable repair challenge for most of us DIY-ers. Just wondering.....what secrets did the AR factory implement to accomplish this connection? And yes, it is pretty funny that we are still fussing over these relics.

To fran604g, your being able to salvage the damaged tweeter was the major accomplishment. Re-cap, re-foam, clean the pots and put 'em back together with an all-around clean-up and I'd guess you'll be plenty satisfied. My comment and question about the exposed tweet/mid wiring was only curious in nature, and was not meant to suggest yet another project-within-a-project or to prolong completion of your restoration. Like yourself, I, too, normally embrace the "keep-'em-authentic" maxim, as much as it serves your intended objective and is practically feasible, but sometimes we can't resist a little extra tinkering. Keep us posted on further progress.

[fran604g]

My comment and question about the exposed tweet/mid wiring was only curious in nature, and was not meant to suggest yet another project-within-a-project or to prolong completion of your restoration.

I took it in the spirit you intended, I appreciate your input, thank you for the compliment, ra.ra.

[RoyC]

This is a point of contention for me with my project in particular. I have thought very seriously about swapping the high and mid range drivers, changing the crossovers and pots and keep the original components as relics. I am going to do the resto first, and if I'm not 100% satisfied with the sound, I will consider doing that more seriously. I am kind of an "all original" enthusiast, though, so I doubt I will actually swap things out. I still may try to match the original unit to the "upgraded" however, but it remains to be seen if that is really necessary.

Stay the course....They will be nice when you are finished.

Kent's tweeter replacement (and associated crossover tweaks) are the result of of much work and experimentation to produce an "authentic" sounding alternative. It was not meant as an upgrade to the original design, only a suitable replacement in the absence of a properly functioning original tweeter. The same tweeter can be set up for front-wiring for easy installation with original wiring. The crossover tweaks are mounted to the rear of the tweeter, so no internal changes are required.

The tweeter is the most troublesome and worn of the AR-3a drivers, so you can finish your restoration project and easily deal with any tweeter issue at a later time if necessary. Trying to re-design the 3a on your own would likely be a waste of time, money, and perfectly good AR-3a cabinets.

Roy

[JKent]

Another terrific foto from JKent - - - but unless I am missing something, I think you meant to say your replacement drivers are rear-wired. To me, this is a great-looking update of a very old speaker. Nice work!

OOPS! You're right of course! And as Roy points out, this mod was done because the original drivers were shot. I had one good AR-3 tweeter and one good AR-3 mid, so I modified the whole shebang to make an ersatz 3a. The AR-11 mids are identical, as I understand it, to the 3a mids. The Hi-Vi tweeter mod has been well documented. So I still have the wonderful AR-3 woofers in AR-3 cabinets with new AR-3 grilles but the crossover was built from scratch as an AR-3a and the mid and tweet... well, you know.

[fran604g]

The tweeter is the most troublesome and worn of the AR-3a drivers, so you can finish your restoration project and easily deal with any tweeter issue at a later time if necessary. Trying to re-design the 3a on your own would likely be a waste of time, money, and perfectly good AR-3a cabinets.

Roy

You've got that right! I am very fortunate with the cabinets, and will not ruin them, in fact I have looked them over several times in the last few days, and I'm thinking that all I need to do them is a little light cleaning and some danish oil. I'm VERY happy with these guys. I'm still contemplating the replacement of the grill material, I'm not convinced I need to, yet. I will need to come up with one badge, however.

But, first things, first. I tend to think ahead too much...

I should have the woofers re-coned by the middle of next week, and in between, I'll make sure I take plenty of pictures and post them here for reference.

[fran604g]

I received my surrounds from Msound a few days ago and endeavored to conquer the 2 woofers.

Before I dove into the repair of the woofers, I needed to repair and preserve the labels on the back of each cabinet and came up with a novel (I think) idea: I used Aleene's Tacky glue to attach them, with first carefully cleaning the undersides of the parts of the labels that had come unattached from the cabinets with a moist paper towel. I then, lightly moistened the labels at these areas, applied the glue and with the moistened paper towel, gently pushed the label back in place while reattaching any torn parts in their proper place. I then went back and smoothed it all out with light pressure. Very much like applying wallpaper. After a quick drying, I applied wax paper over the labels with tape to the cabinet to protect them from rubbing and becoming damaged while they are on their backs for removing the woofer and other parts of the project.

Everything went smoothly and I spent most of the day Saturday very carefully pulling them out of the cabinets and removing the dust caps, old surround material, etc. I have 2 somewhat different speakers in respect to the magnets. The one from SN 45696 has never been reconed or refoamed as far as I can tell and indeed appears to be completely original. However, I do believe someone applied some sort of silicone sealant to it at some point as they both had signs of this. The dust cap was very difficult to remove and I had proceed diligently and with great care to remove it without doing damage to the paper cone, because the paper seemed to be fairly "soft" and slightly pliable. I did manage to remove it completely and didn't damage the cone.

Scraping the remaining silicone that was applied to the surround and frame was just as difficult and took much longer than the other driver took. The driver from SN 3A-04125 went very smoothly and was quite easy to remove all of the old surround and dust cover.

Both voice coils are in beautiful condition with no damage to the former and the wires that are under the dust cover are undamaged. From the little bit of winding I could see, the wire was bright and shiny with no apparent damage or corrosion to either coil.

Both cabinets were packed fully with insulation and they both had the linen "Kempac" intact. When I removed the driver from SN 45696, what I saw further indicated to me that this cabinet has never been opened up. The Kempac was pristine and there was a 4"x5" piece of insulation that had been placed between the driver and it's wires, as if it were put there yesterday, completely undisturbed until I removed it!

Re-foaming was a breeze, with only a couple very small areas where the outer edge didn't want to lay flat perfectly on it's own. No problem when the sealant was tacky, it adhered perfectly to the frame. I decided to coat both cones as suggested by Msound, with a dilute solution of the sealant.

All in all a pleasurable experience with no great stress points.

I took many pictures of both cabinets being repaired, but there are far too many for me to post, I think. I am attaching the link to some photos of interest, for prosperity.

http://s1197.photobu...ation pictures/

I am also including this picture of the woofer from SN 45696, as the magnet appears to be different from the ones shown in the repair manual, I thought it may be of interest to someone for their records.

[RoyC]

I am also including this picture of the woofer from SN 45696, as the magnet appears to be different from the ones shown in the repair manual, I thought it may be of interest to someone for their records.

The magnet on your woofers was used on the earliest foam surround AR 12 inch woofers, and is quite common. It was used into late 1971 or early 1972 (serial number 5x,xxx). This woofer usually exhibits longer leads on the surface of the cone than later versions. It was omitted from the 3a restoration guide in error.

Roy

[JKent]

I took many pictures of both cabinets being repaired, http://s1197.photobu...ation pictures/

Nice job Fran! Love the photos!

Kent

[fran604g]

Thanks Kent and Roy for your comments! I'll keep 'em coming when I get into the xovers next week!

[xmas111]

Nice job. You'll going to love those speakers.

Look forward to see how you make out with the xovers. You certainty have the patience and skill required for it.

John

[fran604g]

I just removed the backs of all 4 rheostats, and this is what I found, 3 out of 4, NOT BAD!

The all original cabinet (SN 45696):

The modified cabinet (SN 3A-04125):

[fran604g]

Out of curiosity, have any of you folks ever tried electrolysis for removing the corrosion on these pots? I just read a very interesting and simple plan using a 12V walwart and a solution of water and salt, then neutralized with soda and water.

I'm very curious if it will cause damage to the fine wirewound resistor?

[JKent]

Never tried it but it will probably work. You can also use a solution of lemon juice & salt, without the wallwart. Pretty sure white vinegar & salt works, too.

After neutralizing you may still need to polish with a wire wheel in a dremel, or with very fine sandpaper. A final coat of dielectric grease or De-Oxit is good.

Even after the pot "looks" good, there may be dead spots. Check with an ohm meter. You should go smoothly from 0 to 15. Analog meter probably is preferable.

Keep up the good work.

Kent

[fran604g]

Thanks Kent, I've used vinegar and salt with a brass brush before on the AR4x pots, and it works well as noted. I am hoping I can clean these up without removing them from the xovers. Maybe I can get my dremel in there, I'll give it a shot, just really fascinated by the thought of electrolytic fun.

[JKent]

They are easy to remove and replace IMO and much easier to clean outside the box. Be sure to note where the pin on each pot leaves a dimple in the Masonite, and where the pointers on the knobs are (see page 13 of the Restoration guide). If you are retaining the original pots you'll want to keep the location of the "white dot" as well.

Kent

[fran604g]

Thanks Kent, I noticed the screws had put dimples in the shafts when I removed the knobs, so I'll be putting them back on in the same positions.

I managed to get the worst one cleaned up.

I tried a brush first, but it wouldn't even touch the corrosion, so I started with a sanding disc to remove the tough stuff, and that worked, but there was a lot of pitting, so I used a light stone in my dremel, followed up with a brass wheel and got the surface as flat as I could. No more oxidation, though. I tried the electrolysis on the wipers just for giggles and sh*ts, it worked really well, after about 4 minutes, I removed it from the solution and the tarnish wiped right off.

I noticed there really isn't much silver plate left on the ones pictured (SN 3A-04125,) but the originals in SN 045696 only needed light cleaning, so they cleaned up like new.

I sprayed them with deoxit, and put them back together. I attempted to measure with my POS DMM, and the really crappy one is working, I got a range of 2.5ohms to 20.6 ohms. Maybe not the actuals, but indication is that it works, and only a couple of minor dead spots.

A couple more pictures:

The wiper doesn't look great in the picture, but, it was really nice and shiny in better lighting. The darker spots are the copper core. Disregard the one on the right, I hadn't gotten to it yet.

[JKent]

the discs are kind of eaten away. Have you considered L-pads?

Kent

[fran604g]

Yes, I have, but I'd like to see if I can salvage these pots. Maybe they're a lost cause?

I saw a post where somebody replaced them with the Ohmite 8ohm pots and built a box around them, also.

[RoyC]

Yes, I have, but I'd like to see if I can salvage these pots. Maybe they're a lost cause?

I saw a post where somebody replaced them with the Ohmite 8ohm pots and built a box around them, also.

I would not use those pots. Regardless of the means to remove the heavy green corrosion (mechanical means are the best), the pits underneath will remain to some degree. The task of removing and cleaning the controls requires too much work to do it frequently, imo. Readings of 20 ohms are too high. Some of the surfaces are not clean enough.

The Ohmite pots are 16 ohms (not 8), like the original AR pots. 8 ohm L-pads work satisfactorily as well, and can be tweaked to act like the original pots for purists.

Both options will last much longer and perform much better than the specimens in your photos. :-)

Roy

[fran604g]

Oh, OK. The Ohmites are 16ohm. I was thinking they were 8ohm like the L-pads. Cool. I'll have to look into those, then for sure. I would rather not use L-pads.

Thanks Roy, for pointing out my error.

[JKent]

You will need Ohmite no. RHS-15R Model H 25 watt 15 ohm.

They are over priced IF you can find them, and making a suitable enclosure that won't decrease the cabinet volume is a pain. But it can be done. I used a plastic project box: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=5980 Others have built small Masonite or aluminum enclosures.

$30 each from Newark: http://www.newark.co...-25w/dp/01F7551 or ebay http://www.ebay.com/...8307#vi-content

$40 each from Mouser: http://www.mouser.co...pPMAPgy6ILlkvMn

I bought some from Skycraft Surplus a few years back for $8 each. Shoulda bought more

Kent

[fran604g]

Thanks for the links, Kent. $8 ea. would have been a nice investment, for sure. As always, hindsight is 20/20.

As far as the internal volume goes, I like the idea of removing the huge dual cap and using that lost volume for the enclosure. I think I will replace the pots after all, when I do the crossover.

In the meantime, I'll have to wait till I have some cash for the next phase. I'll make sure to update my progress when I proceed!

[fran604g]

Well, once again, I couldn't live with not fixing that pot, sooooo, I removed it, detarnished it in my little electrolysis rig and proceeded to flow solder onto the entire flat surface and "button" end of the rivet that holds it together. Then, I very carefully and painstakingly machined the surface flat with a stone in my dremel. I then took a clean cloth, saturated with deoxit, and cleaned vigorously until all was very shiny and bright.

I now have a like new functioning pot that goes smoothly from 0.3 ohms to 15.8 ohms (checked with my POS DMM.) NO dead spots, NO jumping up or down in value.

I did this partly because I'm so damn stubborn (not to mention broke,) and partly because I want to see how long it functions like new. Call it an experiment for posterity.

[HarryM]

Yea,stubborn's a good word.LOL.

I'm going to replace the pots in my 4x's and my 3a's with lpads,even though both pairs looked like brand new when I opened them up they didn't work and after I cleaned them they did work but now they quit working again.

Good luck with your pots,I hope they keep working for you .I'm just not stubborn enough to fix things more then once.LOL.

[fran604g]

Thanks, HarryM.

I was even considering rebuilding the pot, I'm a machinist by trade, so I don't think it would be difficult. All I would have to do is source out (or make) the correct dimension brass washer and rivet, build a small jig for setting and staking the rivet and I'd be in business. I just really like the idea of reusing anything I can if it can be made reliable. I know what I need to do if or when the pots fail again and it's no big deal to open the cabinets up and tear into them again, IMO.

I guess in a way, this is a shortcut for me to start enjoying these 3a's.

Maybe if I were planning on selling them, I would do the replacements up front. Of course with my inability to be satisfied with things for very long, those changes might only be a couple of weeks away, LOL.

On another note, I bought 2 Dayton 6.2uF metalized polpro caps, 2 each of the 150uF and 50uF NPE caps and some 1/8" x 1/2" gasket tape tonight, so I should be hearing sound out of these puppies in a few more days!