AR-4x: unfamiliar crossover

[ra.ra]

Uh-oh. Just when I began to think I knew something about the groundbreaking AR-4x speakers, another version shows up to confound me. I recently began to deconstruct this pair of 4x's for restoration, and soon ran into some unfamiliar surprises. So before I go any further, I thought it would be best to seek out advice, experience, and opinions from the more knowledgeable minds that participate in this forum.

This is a very nice pair of speakers that I recently obtained locally. Unlike my other walnut veneer 4 series speakers, these cabinets were originally unfinished pine and have since been painted white. The consecutive serial numbers are FX-38643 and 644; the woofers are dated March 1966 and the tweeters are dated February 1966. DCR for both tweeters is 4.4 ohms and the woofers are both close to 5.0 ohms.

The woofers are similar to the 8" woof in the AR-4; and the tweets are the typical 2-1/2" cone tweet, but it is the crossover circuits that baffle me. There are several differences that I have not seen before. First, the choke appears to have the number 265 noted, which has no correlation with the number of turns that have appeared in spreadsheets on this subject that I have seen (AR coils). Second, this speaker seems to have the two drivers wired in-phase, whereas more typical 4x's have the tweet and woof wired out-of-phase. Third, what's going on with the capacitor(s)? Three wires, not two, including one to the woofer? Capacitor is wax block type covered with Kempac crepe and dimensionally larger than the typical 20 mf from Industrial Condenser. Also, I have to assume this metal strap over the cap block is a conductive part of the circuitry? Huh?

Procedures I had originally planned to do:

1. Replace capacitor(s) - what value(s)?

2. Remove, restore and replace tweeter controls.

3. Re-dope woof surround and closely inspect tweets.

4. Maybe work on cabinets (strip paint?).

5. Grilles w/badges are decent, no immediate plans.

First pic is meant to show drivers; second pic (v.3) is the perplexing circuitry; third and fourth pics (v.1 and v.2) show 4x crossovers that are more familiar to me.

Help, advice, random thoughts?

[JKent]

Not sure where I got this and it doesn't answer your questions but I thought you may find it interesting.

The metal strap is just a bracket. That's what was in my 4x and 3. You'll have to wait for Roy or some other expert to answer your other questions.

VERY odd that the consecutive SN speakers are so different. I think if I were doing it, I'd use 20uF caps and #5 coils in both. Do you have a LCR meter? The odd coil could be unwound or have turns added as needed to make a #5.

Kent

AR4x speaker comparison.doc

[ra.ra]

Thanks, Kent, that document is a handy little reference I've never seen before, and it seems to be a pretty decent attempt to categorize a visual history of various 4x iterations.

That first model shown is quite rare, and a pair of them sold a few days ago on the auction site (see attachment), and they attracted a lot of attention and a sale price of almost three bills! That second model, sitting on the amp, appears visually identical to my early AR-4's. The third model shown (49XXX), referred to by the author as an "Early-early version", appear identical to the speakers in question for this post.

[RoyC]

ra ra,

I have seen early 4x crossovers like the one in your photo with a cap (20uf, I believe) across the woofer as well as the usual 20uf cap in series with the tweeter. The dual cap and coil differences are probably due to the use of the AR-4 woofer in the early 4x. What are the values printed on the dual cap? I'm guessing it will be a 20uf X2 cap. The metal cap strap does appear to be part of the circuit, putting the 265 turn coil in series with the woofer.

I've edited this post... I previously recommended replacing the crossover caps in kind. After re-reading your first post, it is obvious the drivers are the same, so I agree with Kent. It would be easier to use the later single 20uf cap and #5 coil crossover in both cabinets. Before you do that, however, it would be interesting to hear the difference between these two specimens.

I have extra #5 coils if you need one.

Roy

[ra.ra]

Thanks, Roy and Kent, and I notice that you've both edited your original comments since I viewed yesterday. I believe I need to be a bit more clear here with my situation, since it appears that by providing so many x-o pics I have confused my own main question. In my OP, I was trying to show this new 4x x-o against two "more typical" 4x x-o's. Most sorry about the confusion.

The two white speakers with consecutive s/n's shown in my first pic are indeed physically identical in every characteristic: cabinets, grilles, drivers, stuffing and crossovers. For clarity, I have provided re-labeled jpeg pics of the identical crossovers.

I haven't touched these beyond what you see here, so I cannot yet answer the question about the cap value(s), but Roy's first comment about each speaker having two caps seems to be what the wiring suggests, and it is good for me to have it confirmed that this metal strap is indeed part of the circuit.

First, how best to get at this wax block cap? The rusty rectangular lock washer holding down the coil, I assume, can be removed with various pliers, but I have no idea how to unfasten the small flattened studs that are securing the metal cap strap (with the wire connections). These appear to be some type of rivet inserted from the hidden face of the masonite during x-o assembly. I think that if I might end up having to install two 20 mf caps in each cabinet, I'd probably like to remove this massive wax block and possibly straighten this up a bit and maybe even eliminate the metal strap by re-directing the right hand coil wire.

I hope this description is more clear. These two speakers are identical.

[JKent]

Sorry. I confused things for Roy and you.

So since they are identical, go back to Roy's original recommendation to rebuild them with the same values.

The"speed nut" or Tinnerman nut can indeed be removed with pliers. You may have to pry up the flap part. Wear safety glasses! If you break that thing or the aluminum post it;s on, no biggie. Here's something I found on the web:

"When you first remove them, gently pry up the pins all around, with a small slot-type screwdriver, until you feel the tension easing up, The nut should lift right off."

I would try to drill out the rivets. From your photo it looks like the metal bracket just provides continuity between the black cap wire and the coil wire. You can probably just join them directly together.

Will be interested to know what the cap values are.

Kent

[RoyC]

You may be able to tap the cap block out from under the strap after snipping the cap wires.

Roy

[ra.ra]

Great advice from both of you. Tinnerman nut? That's a new term for me - - - you learn all sorts of handy things on this forum.

Re: wax cap block, I think I will tap first, drill second. I have sometimes wondered why these rivet-like things were ever used instead of a simple screw with an accessible head, but when you imagine the sequence of production, these crossovers were probably mostly assembled on their little 1/8" masonite panels and then later attached to the cabinets with some goo and staples. The masonite is far too thin to adequately accept a screw thread, so I guess another type of fastener was necessary.

I hope to report back within a few days. Meanwhile, a couple of more pics of these speakers, including a close-up with hints at the unfinished pine.

[dynaco_dan]

Thanks, Kent, that document is a handy little reference I've never seen before, and it seems to be a pretty decent attempt to categorize a visual history of various 4x iterations.

That first model shown is quite rare, and a pair of them sold a few days ago on the auction site (see attachment), and they attracted a lot of attention and a sale price of almost three bills! That second model, sitting on the amp, appears visually identical to my early AR-4's. The third model shown (49XXX), referred to by the author as an "Early-early version", appear identical to the speakers in question for this post.

4x ebay.jpg

Hi there

Interesting seeing the $155.00 s&h cost as well.

When I was rescuing AR-4 series speakers off ebuy, the usual USPS economy cost was around $40 - $45.00 a pair from the continental US to Vancouver BC.

[ra.ra]

I totally agree with Vern. That s&h cost for those rare 4x's was way, way excessive, but I have no idea how this all washed out for the eventual auction winner. I have occasionally been an infrequent buyer from this auction site, but never a seller, so I wouldn't know how to estimate the s&h charges. Anyone who frequents that site would agree that s&h estimates are all over the map.

[alkermes]

Dumb question I suppose...could you just cut the wires and leave the old cap in place? Or do you want to clean it up inside?

Do you plan on refinishing the cabs?

[ra.ra]

Possibly my favorite sentiment in this forum is that there is no such thing as a "dumb question", and believe me, I've proffered my fair share. And yes, the old cap could certainly be left in place and who knows yet, maybe that will end up being the solution. Still, my preference would be to remove the wax block in order to: 1) eliminate a bit of unnecessary weight; 2) regain a bit of internal volume that will be then filled with two new caps; and 3) create more surface to secure the new caps to the cabinet. Basically, I'd like to create a neater arrangement.

On the cabinets, I don't know yet what I plan to do. Initially, I almost lost interest in these speakers when I first learned they had been painted, but I became more interested when I surmised they were relatively early models - - - plywood cabinets and old-style woofer were the hints I noticed. Oddly, the white cabs have sort of grown on me a bit, and from all appearances, my guess is that the paint is a heavy duty oil-based alkyd enamel, which I would imagine has a tenacious grab onto the original unfinished pine. I would love to have a pair of blonde 4x's, so full-fledge paint stripping (chemical first, abrasive second) is an option, but once you start down that road there's no turning back, and I haven't yet made that commitment.

[JKent]

plywood cabinets ... the white cabs have sort of grown on me a bit, and from all appearances, my guess is that the paint is a heavy duty oil-based alkyd enamel, which I would imagine has a tenacious grab onto the original unfinished pine. I would love to have a pair of blonde 4x's, so full-fledge paint stripping (chemical first, abrasive second) is an option, but once you start down that road there's no turning back, and I haven't yet made that commitment.

Something to consider: If the cabinets are plywood the grain may not be that attractive. You could clean them up, sand lightly and re-paint them. Another option might be to sand (not too much) to expose some raw wood but leave white in the pores and grain. You'd end up with a "pickled" finish that can be attractive. I used Minwax Pickled Oak stain on the knotty pine paneling I installed in the house to keep it from yellowing with age. If you like the look you could use some Minwax wipe-on poly over it.

Just a thought....

Kent

Oh. One more thought: The linen doesn't make it on the white cabs. I'm pretty sure 1-2-3 Stitch has our favorite 18 count linen in colors other than lambswool. You could make some cool retro grilles in a funky color. I could see "Nordic Blue", "Lily Pond", "Tropical Orange" or others....

[ra.ra]

"The linen doesn't make it on the white cabs."

Ouch. Kent is dissing the aesthetics of my cabinets! Seriously, though, I have to admit that against the white cabinets, the discolored linen really does look extra dingy, whereas with a walnut cabinet I might find the linen to be merely "aged", or to have developed a rich "patina".

I think it was on this site where I once saw a pair of AR-7's that had some Jackson Pollock painted cloth grilles, and I alternated between being amused and being appalled. My own tastes in home decor are not yet ready for tropical orange, so I'll probably try to find a way to stick with raw linen.

I agree that the look of the original plywood might not be that attractive, which is largely why I am apprehensive about beginning the stripping process. However, I do think that the pickled look could be an acceptable middle ground if it comes to that. Meanwhile, I've begun to build a little more confidence about the potential prospect of achieving an attractive "raw" look, as evidenced by these AR cabinets.

[dynaco_dan]

Hi there

I have not posted the step by step job I did on stripping a pair of Dynaco A-50's.

They were heavily painted with a primer and paint, with lot's of overspray of course.

I bought a non-toxic paint stripper and gently scraped off the paint, with the grain, with a flexible metal paint scraper.

Being gentle and no sanding and I found a beautiful grained walnut veneer underneath.

There is also a pair of pine AR-4X's here that I rescued, which are painted, awfull too, which will be another stripping job on my to do list.

Slow and gentle.

Good luck with your choice.

[JKent]

Vern makes a good point. I've used an orange paint stripper (Citristrip maybe). It works well but you must be patient. Leave it on the wood at least 1/2 hour then scrape with a plastic (or if really careful like Vern, metal) scraper. After the 1st application you may be left with that "pickled" look.

You might also consider black grilles. Keep us posted.

Kent

[dynaco_dan]

Hi there

To add to my earlier write-up.

Prior to my doing the A-50's my daughter introduced to what I thought was plastic scrub pads for washing dishes.

She told me they were sanding pads for gyproc mud.

They worked.

None or extremely low abrasion.

[DON]

I have a pair of AR2Axs that were painted black. Removing the paint was fairly easy and because the wood is walnut veneer there wasn't a lot of paint in the grain. I had to do some light sanding and the cabinets look very nice and are just waiting for me to finish. I think I'll just try an oil finish because that's what every AR speaker I've owned had as the original finish. Pine is a whole nuther story! The grain is soft in spots and hard in others and soaks up stain differently. Pine can be stained but best results usually require a sealer as the first coat. The blonde cabinets have what looks like a different veneer on the tops.

[dxho]

I have some AR2s that are shiny. Sometime in their life water had eaten through the lacquer, so I bleached the stain and refinished them. The original color and finish is on the right. I wasn't able to get all the stain out.

[ra.ra]

Lots of good thoughts here - - thanks - - but I'm still not sure what I'll do with these cabinets. I think I have tried that citrus paint stripper before but did not find it very effective - - - maybe I wasn't patient enough to give it time to do its work. I've had good success using more aggressive paint strip products even though the chemicals are dangerous and nasty - - - good ventilation is crucial. FYI, attached is a pic I found of some pine 4x's, and I think I like this lighter look - - - depends on the grain, I guess.

But back to the crossover issue. After some struggle, I was finally able to get this strap off of the wax cap block. At first I tried gentle tapping (thx Roy), but the wax block soon began chipping apart and there was little room for tap-tap movement. Next I tried drilling (thx Kent) and at first thought it was futile. However, with perseverance and changing drill bits, I was able to loosen these connections enough that I could pry/pull the straps from their studs. Two pics of cap and crossover are attached.

I have only dis-assembled one of the speakers - - - still one more to go, but I find no labels or markings at all on this wax block. Help!!! What to do next in order to establish replacement cap values? This interesting link attached is another audio thread where the late Zilch found a similar 4x crossover - - - most of the tech talk is way over my head but there seems to be no conclusion as to the original cap values - - - just some estimates.

http://audiokarma.org/forums/showthread.php?p=1368869#post1368869

Any thoughts on how to proceed? Anything more to be learned by carving up the wax block further? All suggestions welcome.

[RoyC]

One of your photos above clearly shows the Industrial Condenser branding. The value of the cap should be right under it (underneath the coil). I am 99% certain it is a 20uf x 2 cap.

Another option is to measure it with a meter. I believe Zilch's measurements were showing 20uf caps, which had drifted higher due to age. At the time he had no previous experience with that crossover.

Roy

[JKent]

No markings. Bummer.

Guess you don't have an LCR meter. They're handy. You can get a cheapie for about 20 bux http://www.amazon.com/Multimeter-Resistance-Capacitance-Replacement-HQRP/dp/B001VD19ZU/ref=sr_1_6?s=industrial&ie=UTF8&qid=1361308990&sr=1-6&keywords=lcr+meter or spend a bit more at MCM or the like: http://www.mcmelectronics.com/product/72-8735

If you want, send me the cap and I'll take measurements. Roy did that for me before I bought a meter. But the meter is handy. You can use it to measure your inductors (L), Caps and Resistors.

I was not thrilled with the Citri-Strip at first either but as I mentioned, patience is a virtue. Let it do its work and don't rush it.

Kent

[RoyC]

I just found a photo I took of a slightly later 4x crossover. The crossover cap is a 20uf/24uf...Only the 20uf side of the dual cap was used in this cabinet. In the earliest 4x's, the 24uf side would have been the one used across the woofer.

Roy

[JKent]

8 of these will cost $4.80 http://www.madisoundspeakerstore.com/surplus-capacitors/10.0-mfd-polypropylene-cap-10mfdp/tyee/

4 of these $1.40 http://www.madisoundspeakerstore.com/surplus-capacitors/2.0mfd/

Recap those puppies for for $6.20. Nice.

Kent

[ra.ra]

Wow, that is a terrific dual response, gents. You've got me all set up before I could even respond, but here goes anyway.

I think Roy's x-o pic explains everything. I have seen one of these dual wax blocks before, where only one of the cap values is used (I found a 4mf/6mf in one of my AR-4's), and Roy's seems to be the exact same size as mine. See pic attached of my cap blocks with no labels - - they are nearly as large as the huge slabs from Stonehenge, except made from wax (the other sides are very similar).

Also, these values seem to validate the measured values in the Zilch post - - - in his speakers, the 20 mf tweet cap drifted to 25 mf; and the 24 mf woof cap drifted up to 30 mf.

Attached is pic of the multi-meter I purchased from PE a year or two ago. It's all I've got, I paid too much, and I've never really liked it. For these mind of measurements, I need clear step-by-step kindergarten help, and this device is anything but intuitive. The instruction manual is horrible, with inadequate diagrams and misguided cross-references, and it was clearly "written" by the Chinese manufacturers who had no understanding for English syntax. I know it measures capacitance, but I have no idea how to make that type of measurement.

Based on this new cap value info, I am including a possible cap combo (see pic 3) for comment, made up from caps on hand. For the tweets, I had planned on using these 20 mf Solen caps; and I had previously purchased a handful of these 10 mf surplus caps based on Kent's value recommendations. Trying to assemble 24 mf for the woofs, I am showing two 10 mf surplus caps plus either a 3.3 mf Carli or a 4.7 mf Carli. Close enough or not? [i had been planning to use these Carli caps to possibly build a 8mf value for testing my 4x to 4xa conversion project, but I may be willing to sacrifice them here.]

Thanks so much, guys. Further thoughts?