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#1 JKent

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Posted 09 January 2008 - 11:09 PM

Picked up a pair of Rectilinear Mini III speakers today for $10. Circa 1969. They seem nice—close in size to AR 7 maybe? Real walnut veneer, although it is kind of beat up on these and will need a lot of patching. Nice grille cloth (kind of dirty), 2-layer like the KLH with a sheer black backing. Three-way system with level controls for mid and high. Nice binding posts.

Some peculiarities: The grilles are NAILED on with what appear to be 6d finishing nails, cut off so they are about 1" long. The whizzer-cone mid (Philips, I assume—there is a number embossed on the cone--2376) is enclosed in what appears to be a 1 qt container like they put egg salad in at the deli (these were made in Brooklyn. Probably a lot of delis <_< ). The woofer has a nice cloth surround. Tweeter is tiny. The stuffing is not fiberglass or rock wool—looks like something used in furniture (?). The cross over has 2 caps of unknown values, but I have asked a friend to measure them and give an opinion. They are marked "XMC" (larger one) and "XTC-M".
Kent

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J. Kent Hollingsworth

#2 joelongwood

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Posted 10 January 2008 - 12:18 AM

Picked up a pair of Rectilinear Mini III speakers today. Circa 1969. They seem nice—close in size to AR 7 maybe? Real walnut veneer, although it is kind of beat up on these and will need a lot of patching. Nice grille cloth (kind of dirty), 2-layer like the KLH with a sheer black backing. Three-way system with level controls for mid and high. Nice binding posts.

Some peculiarities: The grilles are NAILED on with what appear to be 6d finishing nails, cut off so they are about 1” long. The whizzer-cone mid (Philips, I assume—there is a number embossed on the cone--2376) is enclosed in what appears to be a 1 qt container like they put egg salad in at the deli (these were made in Brooklyn. Probably a lot of delis :D ). The woofer has a nice cloth surround. Tweeter is tiny. The stuffing is not fiberglass or rock wool—looks like something used in furniture (?). The cross over has 2 caps of unknown values, but I have asked a friend to measure them and give an opinion. They are marked “XMC” (larger one) and “XTC-M”.
Kent

Congratulations, Kent, nice score! Having not been able to get into mine (the grill is REALLY on there), it's nice to finally see what's inside. My grill is a dark brown, quite thick material. The mid appears to be similar to the Philips mid used in the larger III (both Highboy and Lowboy). The dustcap is different, as it's flat rather than convex, and the surround is slightly different as well. The tweeter appears to be the same as the super tweeters used in those models as well. The deli container is another thing that the Mini III has in common with its larger brethren, as it serves to isolate the midrange driver in them as well.
Be aware though, that unlike the larger IIIs, the Mini is a 4 ohm system.
I'm anxious to hear what you think of the sound. I spent a good portion of the day listening to the Mini IIIs driven by a Harman Kardon 730 Receiver. The sound, to my ears, is a bit laid back, but very smooth and non-fatiguing. It's a speaker you could listen to all day.............and I did. :D

#3 JKent

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Posted 10 January 2008 - 04:20 AM

close in size to AR 7 maybe?


Correction on the size--they are bigger than I thought: 12x19x9. Bigger than the AR7 (7.75x16x6.25) and even a little bigger than the AR4x (10x19x9). Smaller than the KLH 17/20 (12x23x9). The Rectilinear Mini III is a 4 ohm system.
That "whizzer cone" midrange (or one like it) was apparently used in all Rectilinears, or at least the LowBoy and HighBoy. I think it was also used in Dahlquists. My first encounter with the whizzer cone was in an Advent 400 radio speaker. I thought it was a replacement, since I had only seen standard 5.25" full-range speakers in the 400, but maybe Advent switched to the Philips driver at some point? See discussion here:
http://www.classicsp...?showtopic=2936
Kent
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#4 JKent

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Posted 15 January 2008 - 02:38 AM

Thanks to RoyC (one of the authors of the excellent "Restoring the AR3a" brochure):
http://www.classicsp...ring_the_ar-3a/  here is some info on the Rectilinear Mini III caps:
The large cap [XMC] measures about 87 uf and the little one [XTC-M] is about 1.8uf. The Rectilinear IIIs (not Minis) used 2.0 caps so that may be the intended value. It appears that DF is the same as an equivalent modern npe, so it is entirely possible they are still within spec.


J. Kent Hollingsworth

#5 JKent

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Posted 19 January 2008 - 04:38 AM

I replaced the 1.8uF (2 uF?) caps with 1.9uF mylars. Left the 87ish caps. Pots are good--no corrosion like the AR Aetna-Pollock pots. Still working on the cosmetics--had to patch some of the veneer. Will post exterior photos when finished.

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#6 JKent

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Posted 26 January 2008 - 06:06 AM

The Mini IIIs are coming along nicely. Had to do some patching of the veneer as shown in the pics. Replaced the small caps but left the large ones. Tried cleaning the grille cloth while it was still on the frame but that did not work out too well—it's 2 layers, like vintage KLH, with sheer black backing. Finally removed it, washed by hand, pressed it and reglued both layers. We'll see how it turns out. I may have to go with new linen although that's not really authentic for these.

You can see where I had to cut out damaged veneer and replace/patch it. I've also noticed one speaker cabinet is quite a bit darker than the other, so I'm using "natural" Watco oil on the dark one and "dark walnut" Watco oil on the lighter one. In the photos, the more finished one is the lighter speaker in the bottom right photo. The one with the patch (not yet oiled) is the darker one on the bottom left.

Will post finished pictures eventually, but getting closer!
Kent

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#7 joelongwood

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Posted 29 January 2008 - 04:49 PM

The Mini IIIs are coming along nicely. Had to do some patching of the veneer as shown in the pics. Replaced the small caps but left the large ones. Tried cleaning the grille cloth while it was still on the frame but that did not work out too well—it’s 2 layers, like vintage KLH, with sheer black backing. Finally removed it, washed by hand, pressed it and reglued both layers. We’ll see how it turns out. I may have to go with new linen although that’s not really authentic for these.

You can see where I had to cut out damaged veneer and replace/patch it. I've also noticed one speaker cabinet is quite a bit darker than the other, so I'm using "natural" Watco oil on the dark one and "dark walnut" Watco oil on the lighter one. In the photos, the more finished one is the lighter speaker in the bottom right photo. The one with the patch (not yet oiled) is the darker one on the bottom left.

Will post finished pictures eventually, but getting closer!
Kent

Beautiful job, Kent.........as usual. You make me feel guilty for playing mine "as-is." But since they're in my man-cave, the WAF is not an issue, and I can live with just about anything as long as it sounds good. And, to my ears, the Mini IIIs sound damned good.............I'm anxious to hear what you think. :rolleyes:

#8 JKent

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Posted 22 April 2008 - 02:09 AM

Finished! and they do sound nice. I'll post some "after" pics, but I decided to make new grilles. Even with washing, ironing, starching, the old ones just looked dingy. And the panels are only thick cardboard! I made new ones from 1/4" Masonite, glued sheer black cloth on them (like the originals) then covered with Irish linen (like ARs of that period--not exactly like the original Rectilinear).
Kent
edit: 1/8" Masonite would work fine, and maybe omit the sheer black backing for better transparency.
Irish Linen is CharlesCraft from Michael's craft store.

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#9 JKent

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Posted 22 April 2008 - 04:05 PM

Here they are. Lookin' pretty good for $10 speakers. One is still lighter than the other, so I "may" do some more Dark Walnut on it, then again my friend the wood turner says "If you want consistency buy Formica!" There are a couple of patches--most notably one strip along the entire side, visible in one of these. Look at the earlier posts for "before" shots (I'll probably delete some to make room). Knobs on level controls are not original--they're from Rat Shack. Anyone know why the foam around the whizzer-cone mid? Is it to control refraction?
Thanks for looking at this project :rolleyes:
Kent

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#10 ra.ra

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Posted 23 March 2012 - 02:22 AM

Hmmmm ...... four years lag time - - - any chance of reviving this thread?

First, some initial observations. I am very impressed with the build quality of this vintage of Rectilinear speakers - these little guys are heavy, dense, and compact. But actually, despite my calling them 'little' and Rectilinear titling them as "Mini", these speakers are not really so tiny at all. While JKent first likened them to AR-7's and then updated his comparison to AR-4x, these speakers are actually the nearly identical dimensions (albeit 2" deeper) as the AR-6. Even so, while a 4x weighs in at 18.5 lbs. and an AR-6 at 20 lbs., these brutes tip the scale at 25 lbs. apiece.

Next, a couple of questions. When all but one of the other Rectilinear speakers from 1971 have 8 ohm impedance, why was this speaker product designed at 4 ohms? Following this, why does the tweeter cone have 8 ohms stamped on it? And the tweeter cap - - - thanks to JKent and RoyC, I see his measured at 1.8 uf and was replaced with 1.9 uf (where does one find this cap - which brand makes 1.9?), but would it make more sense to pursue a replacement cap of 2.0 uf per the comment that it was a typical value in other Rect. products?

While making comparisons to AR products, it appears to me that this woofer is nearly identical to that in the AR-4x. The basket, cone and magnet appear exactly the same, but this woof has an opaque felt dust cap and an inverted roll profile on the fabric surround. The spider has the same profile, but the material has a different texture and color.

A couple other peculiarities. My version has the dark brown Rectilinear grille cloth over the thin black scrim (2 layers), but strangely, the grille frame is made from two layers of 1/8" masonite. And just like an orphan Rectilinear XI that I have, the woofer is secured to the baffleboard with a rather odd fastener (see pics 1 and 2). No T-nuts and machine screws here - - - this device is basically a headed and threaded nail, punched thru from behind, with threads which accept a standard hex nut. This spike has a dangerous and sinister point which is no fun to work around.

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#11 JKent

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Posted 16 April 2012 - 03:30 PM

Hi ra.ra
Roy sent me the 1.9uF caps but 2.0 is close enough. And if I were doing it again I'd replace the big "maybe 87" caps with new 90 or even 100uF NPEs. I don't trust anything that resembles the infamous Callins PVC caps.
The tweeter is 8 ohms but the overall system is 4 ohms. Not that unusual. The 4 ohm KLH 20 and the 8 ohm 17 used the same tweeter and crossover, just different woofers.
Kent
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#12 ra.ra

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Posted 17 April 2012 - 02:28 AM

Kent:
Great advice, thanks so much. I really don't know much at all about the wide, wide world of capacitors, and it all baffles me a bit frankly. Still, I agree with you that if you have the patient opened up on the operating table, why not check the liver while you're transplanting the kidney? NPE's are so inexpensive, it makes sense to replace both. The thought that Rectilinear may have used a standard 2.0 uF cap in several models sounds logical, so that's what I'll do for the small cap.

The note about the KLH speakers is interesting - - - so paralleling this discussion to AR, why is this not a similar case with the impedance of the tweeter in the AR-3 being the same driver as the tweet in the early AR-2ax? Am I correct that these two speakers had different drivers (although they look the same) based on the 3 being 4 ohm and the 2ax being 8 ohm?

#13 JKent

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Posted 17 April 2012 - 02:48 AM

The 3 (NOT the 3a) did use the same tweeter as the 2ax. Same driver. I can't explain it--for that you'd have to talk to Roy or John.
btw--another cheap way to replace the 90-ish cap would be a whole bunch of 10uF surplus caps from Madisound. They are 60 cents each, so 9 of them (90uF) would cost $5.40 per speaker. Not bad.
http://www.madisound...ap-10mfdp/tyee/
For the 2uF, if you go with Madisound, they have Solens
http://www.madisound...len-capacitors/
edit: They also have very inexpensive 2.0uF surplus caps (0.35 ea)
Kent


Edited by JKent, 15 September 2013 - 07:16 PM.

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#14 fisher400

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Posted 21 June 2012 - 12:09 PM

I have had rect. research mini 111's stored away for a number of years, I hooked them up to my fisher 400 amp and they sound great. but the midrange speaker has come loose, seems to be some kind of glue holding it in place. does anyone know how to fix this. i want to refinnish the cabinets not sure how about going about it....gonna do the fisher cabinet too.
Thanks
Charles.

#15 ra.ra

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Posted 23 June 2012 - 10:43 PM

Hi Charles, and welcome to CSP.

This thread has helped me understand this Mini III speaker much better, and I am about to soon replace the capacitors in mine. Although I have never seen it identified or confirmed as such, it appears to me that the mid and tweet drivers are secured to the baffleboard only with what appears to be clear silicone caulk - - - a chemical bond rather than a mechanical one (screw, bolt, etc.). I don't know exactly when clear silicone became readily available in the consumer market, but these speakers probably date from the very early 70's and I know that silicone caulk was frequently in use in the construction industry by the mid 70's. It is fairly easy to use from a tube (with a typical caulking gun), has some odor which off-gases with the curing process, and is an extremely strong adhesive.

As for the cabinets, I have done many amateur wood refinishing projects but never knew about the Howard's products until I began reading these forums. Now that I've tried the Restor-a-finish, I will always consider this product and wouldn't hesitate to recommend it for your walnut veneer - - - it is what many readers here seem to prefer. It comes in many flavors - - - you may wish to try natural, walnut or maybe even mahogany if you like the enhanced red qualities in some walnut veneer.

#16 ra.ra

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Posted 15 March 2014 - 02:33 AM

Yet another corollary to the post started by JKent which was then resurrected years later. This model of speaker (and others) from Rectilinear Research Corporation do perhaps seem to fly under the radar a bit, and I continue to be very impressed with their overall quality - - robust construction, very good drivers, straightforward crossovers, elegant appearance, and oh yeah ........ excellent sound reproduction. (Not to mention.... very often available for extremely reasonable cost value.)    

 

Recently, I've come into possession of another pair of Mini-III's.....very similar, but slightly different from other pairs noted here. Walnut cabinets are in very good shape, and the grille fabric is the speckled mid-brown flavor. My other pair (circa 1968) has cotton batting for stuffing; this pair has fiberglass (circa 1974). Previous pair had mids attached with silicone adhesive; this pair has mids that seem to be secured with a more rigid, yellowish glue. Not apparent to me upon first inspection, but it now seems that the internal speaker wiring is an unusually heavy gauge, altho' I have not done any physical measurements or side-by-side comparisons to confirm this.

 

Crossover. It has been pretty well documented that the capacitors for these speakers are 90 mf and 2 mf, but this is the first time I've actually seen these striped capacitors with the secret color coding. I don't know anything about this Mullard-Tropical-Fish code, but still I find it rather interesting. Where did these components come from, and why were they coded this way instead of having alpha-numeric labels? Also with these crossovers, are there any advisable maintenance procedures for these 32 ohm pots other than a spritz or two of De-Oxit?

 

The mid-range drivers are nominal 5" Phillips with whizzer cone. Unlike JKent's mids that had (paper?) pleated surrounds, this pair of mids, while ever slightly different from each other, both have rolled fabric surrounds. No ports or intentional air leaks on these speakers - - full acoustic suspension - - so my question is: would it be beneficial for this restoration to include a re-doping of not only the (inverted) cloth woofer surrounds, but also a similar treatment to the  mid-rage drivers?  

          

cabs.jpg  tweets.jpg  x-o.jpg  Tropical_Fish_Color_Chart_jpg.jpg  philips mid.jpg



#17 JKent

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Posted 15 March 2014 - 11:16 PM

Interesting post! Guess that settles once and for all what the cap values are. Wish I'd known this when I still had the Minis!

I assume you plan to replace the unreliable PVC 90uF, now that you know the correct value. Not that you asked but if I were doing it I'd use either a 90uF electrolytic or maybe mix a 50uF 'lytic and four of the Madisound Surplus caps. The Mullard caps OTOH are considered to be desirable and should be retained.

 

There's nothing mysterious about the color coding. I have a handy little cardboard pocket color code guide from Rat Shack that has capacitors on one side and resistors on the other.

 

Here's what Wikipedia says about the color codes:

The electronic color code is used to indicate the values or ratings of electronic components, very commonly for resistors, but also for capacitors, inductors, and others. A separate code, the 25-pair color code, is used to identify wires in sometelecommunications cables.

The electronic color code was developed in the early 1920s by the Radio Manufacturers Association (now part of Electronic Industries Alliance[1] (EIA)), and was published as EIA-RS-279. The current international standard is IEC 60062.[2]

Colorbands were commonly used (especially on resistors) because they were easily printed on tiny components, decreasing construction costs. However, there were drawbacks, especially for color blind people. Overheating of a component, or dirt accumulation, may make it impossible to distinguish brown from red from orange. Advances in printing technology have made printed numbers practical for small components, which are often found in modern electronics.

I'd suggest testing the cabinets for air leakage by pushing in on the woofers, then decide if you want to use Roy's goo. If all the surrounds are cloth it probably couldn't hurt, but it may not be needed.

 

Nice find!

-Kent

edit:

I was baffled by your caps at first. They look like Red, Green, White, Red. Should have 5 bands so they must be Red Red Green White Red, in which case they would be 2,200,000pF 10% 250V, or 2.2 uF.


Edited by JKent, 19 March 2014 - 05:02 PM.

J. Kent Hollingsworth

#18 alkermes

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Posted 15 March 2014 - 11:34 PM

My highboys have the same grille cloth. I love it, reminds me of shag carpet, sideburns and bell bottoms.
Thye also use a similar plastic housing for the crossover and the same pots.

#19 ra.ra

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Posted 17 March 2014 - 03:45 AM

This post about caps only. More thoughts later.

 

While they will never surpass AR's as my preferred speaker manufacturer, Rectilinears seem to be the Rodney Dangerfield of 60's-70's east coast speakers - - - "they don't get no (much) respect!" But at least there are three or four of us here on CSP who seem to have an appreciation.....

 

No question, I will be replacing the 90uF caps - - - can't seem to locate any single 90 uF NPE cap, which is fine, so am thinking about using Erse 40uF + 50uF - - - both their 6% and 10% tolerance caps seem to be superb price values (pennies!!), and are all almost the exact same dimensions. Easy-peezy parallel install. Would not know what to think of mixing NPE with the surplus polypropylenes - - - am curious, what's to gain with this method? As I've noted in other posts, I do like these 10 uF surplus caps a lot and am grateful for having had them brought to our collective attention here on CSP - -  great, great value .... but really, does anyone truly know how long these will last as compared to NPE's? They do measure very accurately when new, but then, what should we expect from this little known Taiwanese manufacturer regarding longevity?

 

I do not mean to knock these caps at all, but these thoughts are from my cynical devil's advocate voice. My experience with these caps to date has been positive, and I expect to purchase more in the future at such a bargain basement price. Despite the attractiveness of their ultra low price, my own replacement solutions are largely driven by a preference for simplicity plus a realistic understanding of my own soldering skill level. Issues of capacitor longevity aside, I remain unconvinced I'd be able to detect audible differences between film and NPE caps, even tho' I do understand the huge importance of the midrange driver in the Mini III and want to restore its function properly. Final point about the multi-cap solution: at what point does a large wad of small cap values begin to compromise the necessary internal volume of a speaker cabinet, particularly with small cabinets?

 

About the 2 uF cap. I had originally planned to simply replace them with a good (Dayton? Erse?) film cap, but with JKent's comment about Mullards, instead I will remove and measure these before deciding on replacement. And the color coding? It does sound fairly straightforward, but there is no way I was able to come up with a value of 2uF for these caps trying to interpret the tropical fish chart.        

 

 

 

  



#20 ra.ra

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Posted 17 March 2014 - 04:21 AM

to alkermes: I first learned of these striped Mullard caps reading a thread on AK about highboys, and my pics below show two of the three grille cloth fabrics (JKent's original off-white being the third choice) offered on Mini III's.

 

to fisher400: your comments in post 14 make sense to me now - - this pair of speakers has the mids adhered to baffles with a stiff yellow glue (that looks similar to Titebond) instead of the flexible clear silicone that was used in my first pair.

 

to JKent: thanks, yes, I will conduct a more serious woofer-push test when I give these a more thorough evaluation. After pulling the woofers to peek inside, I found that the original rope caulk is so crunchy (unlike similarly aged AR's I have dis-assembled) that it can no longer provide even a temporary air-tight seal, so I will have to provide a good temporary seal at the woof opening to conduct this test.

 

Images below show two types of grille cloth, both speckled - - what I call mid-brown and dark-brown. Backside of grilles shows that mid-brown was single layer cloth, but dark-brown also had the second layer of black scrim (note here that position of tweeter has changed). Backside of cabinets depicts two minor, but obvious, differences - - in these pics, more recent speaker is on left; earlier speaker (with missing control knobs) is on right. The first notable difference is the change of speaker wire terminals. The other difference is the cabinet perimeter assembly detail. On the earlier (right) speaker, the back panel is flush with the four sides - - probably a simple rabbeted joint. On the later (left) speaker, the back panel is recessed from the four sides by about 1/4", and while this does provide a nice little finger grip for lifting the cabinet box, I think its primary purpose is to keep the rather large tone control knobs from protruding beyond any part of the wood cabinet box, which does happen in the earlier version.

 

frontside.jpg  grille cloth.jpg  grilles rear.jpg  backside.jpg  backside corner.jpg

 

     






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