AR-6 Restoration

[ra.ra]

Just wondering what happened to the OP's project in this thread? Again, I hope my comments did not confuse you further.

Also just wanted to say that the first pair of AR-6's (....partial, at least ) I ever picked up had already been replaced with a real mish-mash of incorrect and inconsistent drivers - - see first pic attached. Both woofers were the 4x cloth-alnico variety, and the tweeters, while appearing almost identical from the front, were in fact not the same part number and had different sized magnets. They made noise, they played music, sort of - - - but I did not like the way they sounded at all.

So I replaced everything with more correct and matching drivers (second pic). I used the 200001-1 woofers which have the smooth cone, flat dustcap, foam surround, and square ferrite magnet. For tweeters, I used slightly newer part number 200038 (dated 1981) which is very similar to original but might have slightly higher power handling ability. Also, I cleaned the pots and replaced the caps, and now I'm very happy with these speakers.

[Phxjohn]

I am late to this party but I noticed the white coned woofers look exactly like what Klipsch used in the KG 4's. They would never be suitable for a small enclosure. I have a pair of the original design 6's as well as 3a's. In the past, I had 7's. The 7's come nowhere close to the original design 6's for bass response.  

[JKent]

Hey--there's a pair of AR-6 speakers on ebay now for only $1,740.00! Grab 'em!

[ayc868]

Hi,

is it easy to  upgrade to  a original later version AR-6

ceramic magnet woofer +  single chip crossover

?

 

 

 

[ReggaeBen]

Hello all,

Thought I might jump in on this thread as I've just recently bought a nice pair of the Australian version (?) AR6. It won't be until a week or two until then arrive home but I'm told (and praying) that they are all original, aside from the refoam.

They are in nice shape and FYI I paid $230 AUD, I'll have to pay for shipping (100 +/-) but all in all I'm happy.

Can those who've listened to the last crossover version, that being the full range woffer with no cap or inductor and the earlier version(s) mind sharing their thoughts on what they heard? I may consider this if it is worthwhile and I have the correct components to do so.

Gabriel, how are your 6's coming along?

Cheers

Ben

 

[GD70]

Last we heard from Gabriel was Oct 22. I guess he worked them out and had no more questions.

Robert, an amazing amount of information, that will benefit many others with the 6's.

Glenn

[p38arover]

On 10/18/2017 at 11:16 AM, ra.ra said:

Actually, there are three versions of AR-6 crossovers, but we do not need to discuss version C which was used in Europe for later models (it had no coil and employed a two-position switch).

Perhaps four versions.  Mine has a combo of type A and B, i.e., it has the 24uF capacitor and 10 ohm resistor across the woofer AND it has the 16ohm rheostat, not the 3 position switch.

The serial nos. on my two are 006024 and 006032.  However, there a re handwritten letters before the printed S/N, viz. ER or EG.  They were built in the UK.

The 10 ohm resistor in one of the speakers must have been rather warm, it's burnt the sound deadening material.

My woofers don't have a square magnet. and they don't appear to have been changed (I bought the speakers secondhand many years ago).

My speakers also have the narrow front lip mentioned earlier.

Why did I open them up?  I replaced my workshop amp (Harman Kardon Model 630 Stereo Receiver that my daughter has now taken) with a Sony STR-DE525 from my son (he'd discarded it as it had stopped working - I had to replace one of 15 volt  power regulators).  When I switched it on, and with both the electronics workshop AR6 speakers and the mechanical workshop KEF speakers being driven, I noticed the AR6 were severely lacking in treble.  The 16 ohm rheostats in both had gone electrically open circuit.  I pulled them apart and found that they just needed cleaning (a spring clip holds the wire-wound resistance element onto the casing).  I came to this forum  because I was looking for the circuit diagram of the speakers. 

Tonight I'll reassemble them and hope they are working properly again.

Cheers

Ron VK2OTC

[p38arover]

Further to the above, I put an analogue ohmmeter across the 16 ohm pot/rheostat and rotated the shaft from end to end.  The circuit went open circuit at both ends and was a bit erratic along the rotation.

So I pulled it apart (it's held together with a clip).  The brass rivets at each end were black with, I suspected, oxidation.  Checked with the ohmmeter, they were high resistance.  As the pot wiper hit the ends of the track, it would ride up onto the black sections and go open circuit.  I scraped them clean and burnished them with a bit of wet & dry grit paper.  I polished them with an eraser and also polished the centre wiper area with the eraser.  I also cleaned the track.  Reassembled, it was flawless in rotation.

Re the woofers, I suspect they have been replaced.  Why? Because the soldering on their terminals was not good (actually, terrible) and also the 24uF capacitors have glue residue where they had been glued to the speakers but not these speakers.  There's no trace of glue on these.

Tested, the speakers once again have treble. 

[ra.ra]

7 hours ago, p38arover said:

Perhaps four versions.  Mine has a combo of type A and B.

My woofers don't have a square magnet. and they don't appear to have been changed (I bought the speakers secondhand many years ago).

Hi Ron, and welcome to the forum. Your AR-6 speakers pose some interesting questions, and yes, it does appear that they have elements of both the A and B versions. Re: the woofers, I see in your follow-up post that you note your suspicion that these drivers are non-original - - that is correct, those are not original AR woofers ('tho' it would be interesting to see their front side) even though that 24uF cap appears to be a Royalitic which is similar to what I have found in version B speakers.

Re: tweeters, good to hear you've got them working again with the cleaned-up pots, and I'm curious to know if these are front-wired tweeters? Often these speakers can be improved by replacing the original 10uF cap, so it would be helpful to also post a pic of the internal crossover network at least to confirm the circuitry of your pair. Is there one coil or two?

It's impossible to say exactly how your speakers came to be, but I suspect that at some point the original woofers were tossed out when the foams went bad and they were replaced with an alternate brand. How and why the added cap and resistor (from B version) arrived at this solution is anyone's guess, but maybe you have discovered an undocumented version? Post a few more pics and maybe we can figure this out.  

[p38arover]

Thanks for the reply, ra.ra

I'm not sure how long ago it was that I bought these speakers - over 20 years - possibly bought from a Pacific island radio station I worked at from 1990-1993, so they may been bought 25+ years ago. I don't recall from where I got them.

The crossovers have the no. 4 and no. 12 coils and the speakers have the front wired tweeters.  The capacitor is a Royalitic NP

I guess the question is, would they sound better without the 10 ohm/24uF RC circuit?  I assume it's there to roll off the high frequencies that may get through the crossover.  As I've got them apart, it would be easy for me to modify one and compare them (either with a function generator signal source or with music)  but they aren't in a great listening environment, they are in my small electronics workshop/ham shack.

I have too many projects............

[p38arover]

I saw you made comments about the speaker cloth in an earlier post.  Here's mine:

 

[ra.ra]

On 9/27/2018 at 6:50 AM, p38arover said:

I have too many projects............

Sheesh, I know that feeling, too. 

With the exception of the non-original woofer and its added components, it certainly appears your AR-6's are Euro-style Version A, and it's a good bet that the Sprague Compulytic blue can capacitors still measure within spec. The woofer is the only oddball part, and we'll  probably never know how the R and C components from version B ended up here. Without knowing how that woofer is meant to perform, it is certainly worth a try to remove the RC from one speaker and then compare. Original AR-6's were known for delivering excellent bass response from an 8-inch woofer, so without more in-depth testing and measurements, that would be one subjective benchmark to aim for.

From what you've shown us, the cabinets, grilles, and badges all look very good. Quite possible they could all benefit from a little TLC. The badges can be easily polished, and yours appear to still have the protective clear stick-on coverings.

 

[p38arover]

Yes, I'll try one without the resistor/cap.

I've added a pic of the tweeter rear (taken with a mirror and then the image was flipped).

I've disassembled the other speaker's rheostat and cleaned it up.  There wasn't as much corrosion as the first.  I've added pics so that others can see how to disassemble it.  One can see the clip that holds it together.  The wiper arm drops out so it can have the silver contacts burnished with an eraser.

The obvious corrosion on the rivetted terminals doesn't seem to have leeched into the junction of the rivet and the terminal tag thank goodness.

 

 

[ra.ra]

Those fussy pots are annoying, but yours should clean up OK. As added future protection, many restorers apply an electrically conductive metal protectant to all exposed parts before re-assembly - - - De-Oxit, silicone spray, or dielectric grease. The thing I find difficult to work with in this particular crossover is that stubborn stiff nichrome wire which connects to Lug #2.

Your pics are great - - especially the clever one of the tweeter backside. The date code shows fabrication in 8th week of 1974, and you now know that drivers were built in USA while speaker was fully assembled in England. I have learned from experience - - and your picture confirms - - that sometimes these T-nuts have a rather tenuous grip with the front cabinet panel. One solution that I like is to apply a smear of epoxy to the backside while the cabinet is opened up, simply adding another level of connection between metal and wood to insure against material blow-out (see pic).

But still, the woofers are your biggest challenge.   

[p38arover]

Thanks for the reply.  I'll get the epoxy out!

Re Deoxit, we can get here in Australia but, by heck, it ain't cheap!  I have silicone dielectric grease and silicone spray.

Re the nichrome wire, the way AR assembled the speaker makes it worse.  putting it through the rheostat tag then wrapping it around the green wire before soldering makes it difficult to untwist. 

If I bought these speakers from the radio station, it's likely the woofers were replaced by a tech who worked there before (and later with) me.  He was a long-time friend - we were in the same class at the radio technician training college 1965-1968.  I can't ask as he passed away a couple of years back.  He would have bought the replacements from an Australian components retailer.  (The station did have some good gear, I also bought a no longer used Thorens TD125 and SME 3009 arm with a Shure V15 cartridge).

I didn't get the second AR-6 reassembled last night.  We had visitors in the late afternoon and, after he and I finished off a couple of bottles of shiraz, and lots of cheese, dip, and crackers, I didn't feel like going out to the workshop. 

I might take my very old KEF Celeste K2 bookshelf speakers off the shelf in the mechanical workshop and give them some TLC, too.  (My lounge room speakers are Wharfedales)

I do appreciate your taking the time to reply.

Cheers, Ron

[p38arover]

Thanks for the heads up on the badges.  I hadn't really looked at them and just assumed they were discoloured plastic.  There was, as you noted, a bit of plastic stuck onto them.  With a polish up on some 1200 wet or dry paper they look really good with a brushed satin finish  I might need to spray them with clear lacquer or enamel.

While I was in the speakers, I measured the caps and inductors.

S/N 6024

Inductor #4 0.79mH 0.63 ohms

Inductor #12 0.23mH 0.53 ohms

10uF cap 11.74uF ESR 0.12 ohms Vloss 1%

24uF cap 40uF ESR 0.44 ohms Vloss 5%

10 ohm resistor 10.13 ohms

Rheostat 16.13 ohms

S/N 6032

Inductor #4 0.87mH 0.56 ohms

Inductor #12 0.23mH 0.46 ohms

10uF cap 11.47uF ESR 0.19 ohms Vloss 1.1%

24uF cap 40.4uF ESR 0.42 ohms Vloss 4.6%

10 ohm resistor 10.23 ohms

Rheostat 16.23 ohms

Maybe I should have subtracted the measuring lead resistance of 0.07 ohms from those ESR figures.  I did from the other resistance measurements.

Testing with music (DAB radio) tonight didn't show any differences between the speakers, one with the RC network, the other without.  I'll test it tomorrow with an audio oscillator and my imperfect ears.

Now the question of the 24uF caps arises.  Both measured 40uF.  I wonder if that's really a problem and whether I should replace them.

Anyway, the badges before and after:

 

[Aadams]

You may have seen this before but you might want to review this great legacy thread from the very experienced Carlspeak.   I have been reading this stuff for years now and have come to believe if you don't have the right equipment and know how to use it and understand the equations, measuring capacitors is mostly just farting around.    Summation is Carl almost never saw a Compulytic out of spec.  What are the odds that you have two of the same value measuring almost identically out of range?

Adams

 

[p38arover]

Thanks for the link.  I hadn't seen it before.  Very interesting reading.  I didn't test the caps with varying frequencies.  The phase variation was interesting.

However, prompted by your comments, I looked again at my scribbled notes and realised I'd made a transcription error.  I typed the first set of figures then copied and pasted it for the second speaker, updating the measured values but missing the 24uF cap.  It should have read 38uF.  I'll edit my post above.

Today, I went to the local electronics parts store and bought a 22uF 100v non-polarised (NP) crossover capacitor and a 22uF BiPolar (BP) cap.  The latter looks just like a small PCB electrolytic and was 1/4 the price of the NP cap.  When I got home I measured them with the same test equipment used earlier and got these results:

22uF NP 24.83uF ESR 0.23 ohms 1.0 Vloss

22uF BP 24.07uF ESR 0.48 ohms 1.6% Vloss

I also went through drawers of capacitors of all types and measured them.  All, except some very old caps were in-spec, usually high in capacitance, up to 20% high.  The old caps were up to 100% higher.  I tossed them out.

The tester I use is a Mega328 LCR-T4 12846 LCD Digital Component Tester or a similar item

So are the Royalitic 24uF caps in the AR-6 speakers really high in value?  Without Carl's test rig, it's hard to be sure but replacing them isn't expensive.  The question is, what is the effect of 40uF//10 ohm compared with 24uF//10 ohms?

What is the purpose of the parallel RC network?

As an aside, when I was taking the photo of the tweeter with a mirror, I put a torchlight inside the speaker box for illumination.  When I finished I stuffed the box with sound deadening material and buttoned it all up.  The next day I couldn't find my torch.  I looked high and low in my workshops to no avail.  Yesterday, I opened the speaker up to check the soldering on the nichrome wire (it's a pig to solder) and found the torch, dead flat, in the speaker.  :)

[Aadams]

One thing for sure you have been thorough.  I am not the expert here but I can say with comfort  it won't hurt anything to replace the Spragues..  What caught my attention was the near identical variance of the 24 uf caps and they were Compulytics.  I think the tolerance is 10% and those appear to be well out of spec.

EDIT: You said Royalytic in your post and I have been thinking Compulytic because that is what I saw in one of the images.  I think Compulytic and Royalytic were different lines.  Carl was referring to Sprague Compulytics.

Adams

[p38arover]

Sorry about the delay in replying - the thread has been inaccessible to me for the past couple of days.

BTW, I am no expert, just a bumbling ex-electronics tech.

Yes, the Sprague cap is the big blue 10uF item.  The small 24uF is Royalytic (a brand I'd never heard of).

I tried a side by side comparison of the speakers, one with the Royalitic/resistor combo and the other with none with both music and with a sine wave source (from my HP oscillator) and I can't detect any difference between them  Having said that, my hearing is rolling off at 9kHz.  However, as I swept upward in frequency, there were odd sounds coming from both speakers, possibly at the crossover frequency (design value unknown).

I'm yet to do a comparison of the speakers, one with the Royalitic and the other with the new in-spec 22uF cap.

The speakers do sound better than when I started.  I'm sure if I drove them hard, the front speaker cloth panels would buzz as they are warped and are not held tightly into the Velcro.

Cheers

Ron

[ra.ra]

On 9/29/2018 at 12:28 AM, p38arover said:

Re the nichrome wire, the way AR assembled the speaker makes it worse.  putting it through the rheostat tag then wrapping it around the green wire before soldering makes it difficult to untwist. 

I totally agree about that nichrome wire - - it's just a real struggle to work around. Its short length allows for no slack when removing the pot, and it seems to be far more difficult to unsolder and re-solder than other wires in these crossovers. Also, you did great work on shining up those badges. 

First pic here shows two caps recently removed from a pair of AR-6's - - both are 10uF and 50V; bottom is Compulytic by Sprague; top is Royalitic by Industrial Condenser Corp (same mfr. that makes the wax block type), and this cap is almost identical in size to the 24uF Royalitic cap typically found in the woofer circuit. I don't know enough about the properties or construction of caps to understand why they are so different in dimension, but obviously each brand of NPE was good enough for AR to use in thousands of speakers.

In this recent thread about AR-6's, the OP (ReggaeBen) gets a measurement for the Compulytic cap which is very similar to yours, but his project has now made me very suspicious regarding the longevity of the Royalitics. These do not have the same robust build quality as the Spragues, and his test measurements suggest that these should be replaced.

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/10277-australian-ar6s-resto/

Second pic shows the epoxy treatment to reinforce the T-nut connection - - just be certain to not get any into the threads of the nut.

[ra.ra]

Oops, I neglected to include my thoughts about your woofer predicament. What you have is: an original pair of AR-6, Version A, but with unknown impostor replacement woofers which have received an RC modification consistent with the AR-6 Version B. In other words, sort of a mish-mash of components, which initially led you to suggest a possible fourth version of AR-6.  

Since you do not know the exact parameters of these woofers and how they might compare to the originals, adding the 24uF cap and 10 ohm resistor is just a guessing game at this point - - - it is unclear exactly what you are trying to replicate. Your early assessments seem to indicate no appreciable difference with or without the RC woofer circuit, but it sounds like you are still experimenting. This is fine - - even good  - - and I'd suggest that you simply settle on what sounds best to you in terms of overall balance and LF performance, and not necessarily try to re-construct the RC circuit that was intended for a different woofer driver.

Regarding high frequency, the performance should be very good after having cleaned the pots. These tweeters are very nice and have great dispersion. Many people would find your Compulytic cap readings (at roughly 15 and 17% above the 10uF rating) to be unacceptable or "out-of-spec", but I say just keep 'em if you are satisfied. There are many 10uF caps available and these can always be changed later, but I'm not sure how much difference that would make, particularly with personal hearing that is not as sharp as it once was.

[ReggaeBen]

Just a quick mention from me, I did measure my Sprauge cap with both a low cost ESR meter and my Fluke, while I actually do think the ESR meter can measure esr okay (based only upon comparing various resistor measurements of my ESR meter and my Fluke, they were almost identical), however capacitor readings were off compared to the Fluke and of which I'll trust. 

I find it interesting also that you have the rheostat and the woofer with cap/resistor setup, cool  keep up the good work.

Ben

 

[p38arover]

On 10/4/2018 at 4:48 AM, ra.ra said:

 What you have is: an original pair of AR-6, Version A, but with unknown impostor replacement woofers which have received an RC modification consistent with the AR-6 Version B. In other words, sort of a mish-mash of components, which initially led you to suggest a possible fourth version of AR-6.  

I'm not so sure.  Had the 10 ohm resistor and 24uF cap been of a different brand to the original, I'd agree.  However, the cap had glue on it from where it had been stuck to an original AR woofer.  Who would look around to find secondhand original components to change a set of speakers?  They'd use off the shelf components (I would).

Re the 10uF cap values, I don't believe the variation from 10uF is all that significant with respect to the sound.  Ditto with the new 22uF cap vs the 24uF (err, 40uf?) cap especially considering the woofers aren't original spec.

I really appreciate your comments.  I hadn't seen ReggaeBen's thread so that made interesting reading.  Thanks to you, too Ben.

I'm pretty satisfied with what I now have but I will get some teak oil and give the cabinets a once over.  Quite frankly, my speakers are in far better condition than others I've seen on here and I'm only using them in my garage workshop (like I am with my KEF Celestes).  I feel I'm committing heresy!

I think I mentioned earlier that my daughter is taking my Wharfedale 2180 bookshelf speakers (I bought those new in 1991/2) but I'll still have the Wharfedale Valdus 400 towers (got them from my late son in 2008) in the lounge room.

Cheers

Ron

[ra.ra]

11 hours ago, p38arover said:

I'm not so sure. Had the 10 ohm resistor and 24uF cap been of a different brand to the original,.....

Yeah, this is indeed the mystery here, and I'm just speculating with my theories. Exactly how those particular RC components (i.e., Royalitic cap) ended up on that impostor woofer is something we'll never know, I suppose. One other random question here: if you are unable to detect performance differences between with-or-without the RC circuit, why include it ?.....particularly if it looks like it has already burned the cabinet stuffing?

About the cap measurements - - - I am strongly inclined to agree with you that detectable differences to our ears are probably not appreciable if the cap values were more closely matched to original spec values. My point was that many people get way too woofed up about this issue, and while I understand that the original design is very important, there should be sensible limits regarding the extent of restoration efforts to keep these old speakers alive and kickin'.  

Sounds like you've got a collection of fine loudspeakers, and you're a lucky man when the AR-6's get relegated to garage duty. The cabinet oiling process always provides immediate gratification, so it sounds like you're in the homestretch.