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Another AR-4x restoration


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These were mentioned in Post #37 here: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=8414&page=2

My very first speakers, which I still have, were AR-4x's purchased new in 1969 from Sound Reproduction in East Orange NJ for $88.00 (I still have the speakers AND the receipt!). Those are SN SN FX262692 & FX262765.

The ones for this project are earlier: SN FX127823 & FX12815. They were a thrift store find and in amazingly good condition. The grilles are near-perfect, one logo is missing, there are 2 or 3 small chips and one larger one, about 3/4".

Yesterday I worked on SN FX127823 so here are some observations:

I'm sure these were never opened. Getting the grilles off was a bear because of the long staples used to hold them on. There was a LOT of duct seal used on the woofers and tweeters but it was still soft(!) so it was easy to remove. The woofer is like the ones in my other 4x's, not the AR-4 style with "tic-tac-toe" on the cone. The Kimpac was intact but to my eye it appears the stuffing was rock wool. OTOH the pot, which can be badly damaged by rock wool, was in great condition.

Not sure of the exact production date but according to Roy the earlier ones had 17 oz. of fiberglass and used the #4 (0.88mH) inductor. Later AR went with 11 oz. fg and #5 (1.2mH) inductors. Apparently AR at some point reduced the amount of fiberglass and increased woofer inductance to raise Qtc in the AR-3a and followed the same formula with the 4x. I weighed the rock wool and it was 19 oz. I happened to have the stuffing from some KLH 31s that were too far gone to restore. They're about the same size as the 4x and each 31 had 13 oz of pink fg per speaker so I just used that. Also, the KLH used an open-weave fabric that is more durable than Kimpac so I used that as well. I kept the stock #4 inductor.

The pot was cleaned with some contact cleaner and a Dremel wire brush, coated with dielectric grease and reinstalled. The 20uF wax cap was disconnected and replaced with a pair of the ever-popular 10uF surplus caps. Some of the wires were replaced with slightly longer ones just for convenience and the woofer wires were terminated with Stakon tyle crimps, just in case I need to open it again. I used the convenient sealing caulk from PE.

Cabinets were wiped down with lacquer thinner to remove years of grime. The small chips were filled with epoxy/Mixol brown filler and the large chip was patched with a piece of veneer. btw, these cabs have plywood backs (my others are particle board). The backs are in very nice shape, marred only by some screw holes used for hanging.

I opted not to sand these. The cabs are in very good shape and I don't like to take sandpaper to veneer if I don't have to. Besides, there were a couple of thin spots on corners where the light substrate was peeking through.

For final finishing, the cabinet was wiped with Howard Restore-a-Finish in Mahogany. This is just a personal preference but I like the slightly reddish cast it gives walnut speakers. Final finishing will be a couple of coats of Watco Medium Walnut Danish Oil.

Here are some photos so far. "Before" shots are in the post linked above. More to follow.








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Fine work as usual, Kent, and I also have a similar preference for highlighting the reddish tones in the walnut. Nice simple cabinet prescription - - lacquer thinner cleaning, RAF blending and toning, followed by Watco. Also, always glad to see the little "inspector guy" stamp on the inside of the cabinet (pic 5).

Couple thoughts/questions. Looking back at your "before" pics, it appears the woofer surrounds have different coloration (one black, one not) and I'm curious if maybe some of the original butyl treatment has flaked off - - - any plans to re-dope these, or are they good "as-is"? About the stuffing - - I tend to not be too fussy about this matter, but your use of the 13 oz. KLH fg is close to a 25% reduction from original 17 oz., and that just might have be enough of a change to have an effect on LF performance.

Also about the stuffing - - - I know I'm in the tiny minority on this, but on more than one restoration project I've simply re-used the original rock wool. My recollection from following years of threads on this site is that "the jury is still out" on whether rock wool actually contributes to accelerated corrosion of pots. I've read the expert members' posts which established this theory with documented observations, but I've also seen other expert members subsequently question whether there is a cause-and-effect relationship. Yes, the rock wool is relatively nasty stuff but we need to remember that it is the pot, and not the stuffing material, that is the typical weak link here. It appears that your pair - - having rock wool, never opened after close to 50 years, with pots in good condition - - would tend to be an excellent case study which challenges the notion that rock wool increases the likelihood of significant pot corrosion.

Great project, looking forward to further pics and observations.

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Photo 5 shows the little inspector guy Robert refers to. Insides of these old cabs usually have some little stamp on the wood.
I think any solvent can be used to clean off grime: Lacquer thinner, alcohol, paint thinner. I've also used Spray 9, a strong cleaner similar to Fantastik but stronger.

Thanks for the positive comments.
The lighter woofer surrround is on the other speaker and I'll check it out. The surround on this one seems fine. Don't want to over-do Roy's glop although I have some on hand if needed.

I hope to hear from Roy on the stuffing issue. My thinking was the "revised" version of the 4x had only 11 oz of fg so I thought the 13 oz may be a step in the right direction but of course I still have the #4 inductor so I'll leave it to the more technically minded to advise me.
Your comment about the rock wool "sounds" logical to me but I'll defer to our resident scientist, Prof. John O'Hanlon, who wrote in the 3a restoration booklet that rock wool "is full of impurities including sulfur" and stated "you should use fiberglass if at all possible." Besides, as you said, rock wool is nasty stuff. The fg is nice and clean ;)

Attached are some repair photos. The long skinny chip was filled with brown epoxy and looks better "in person" than in the close-up shot. The veneer patch is hardly noticeable.




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Nice job, Kent, especially the veneer patch.

I was thinking of starting a thread on my "silk-purse" AR-4x's but glad I didn't. They are from earlier production than this set.

I'll wait until they are further along since it is a bit of a drawn out project I'm not sure I can finish soon. They also had the rock wool stuffing.


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Thanks Roger.

One finished! Photos show:

  1. The front, with the original grille and my reproduction logo.
  2. Left side
  3. Right side
  4. Bottom. There are some dings, but not bad and it's on the bottom.
  5. Top front corner, showing the most "serious" defects: a small hole from the staple, the long thin epoxy patch on the front edge and the veneer patch on the back corner. None of these are noticeable indoors unless you get up real close.
  6. Braces where the frame cracked. Looks crappy from the inside but fine from the outside. These were epoxied in place, with some wax paper behind them to protect the clot, so the cloth was not removed.

btw, the grille is just pressed in place with a friction fit. I had thought of using one small piece of Velcro but I don't think it's needed.

Now on to the other one....








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Nobody will really notice those minor nits if you don't leave those bright yellow arrows on the speakers...


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Kent - Congratulations on finding that great deal on the AR-4ax! And thank you for posting the renovation of the same. Do you have a before photo of the crossover so that we can follow the progress? I always get lost in translation.

It is nice to see one of my tutors at work again!

Best Regards,


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Thanks Greg.

The "before" shot of this one isn't that clear but I'm attaching a before shot from my first pair, labeled by CSP member johnieo.



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Great stuff again Kent! Any feedback on how they are sounding?

VM, yeah lacquer thinner and mineral spirits (for less smell) are a great way to get all the build-up off and back down to earlier layers to expose more of the grain and lighter color. I typically use some 400 grit wet/dry sand paper with it. You should see the gunk that comes off. Many of the surface scratchs fade away as well on most. I figure why try to put new finish product, whether it be oil or Restore-a-finish, on top of the layers of gunk that are on these. Many have been exposed to cigarette smoke and products like Pledge over the years.

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