Restoring the AR-3a

[totsuka]

Got it. I hooked them up and both actually worked. I feel bad the seller did not know. Got one speaker grill off...a bit of a struggle...but did not break it and followed the screw method....plastic frame still intact...

[Brad1234]

I am working on recapping my early model AR-3as following the Restoring the AR-3a Document and cannot find a 0.27 ohm 20 watt non inductive resistor anywhere for the mids and woofers. I have found the ceramic wire wound kind, but not the audio quality non inductive kind. The closest non inductive one I can find is .22 ohm or .33 ohm. Does the non inductive resistor really make a sound quality difference on mids and woofers over the basic wire wound kind??  Any help with this is greatly appreciated, this will be my first crossover rebuild so learning as I go. Have read some places that the wire wound resistors work fine for low ohm ratings?  
Brad 

[lARrybody]

These are my favorite resisters to use on my AR speaker recaps. A little expensive but the quality is there.

https://www.partsconnexion.com/MILLS-68107.html

Or you could use two of these in parallel

https://www.partsconnexion.com/MILLS-66130.html

Edited February 7, 2022 by lARrybody
adition

[Brad1234]

I saw those when searching for them online, but is 12 watts ok when the restoration doc calls for 20 watts?  

[lARrybody]

1 hour ago, Brad1234 said:

I saw those when searching for them online, but is 12 watts ok when the restoration doc calls for 20 watts?  

In my opinion the 12 watt resisters would probably be fine. You can parallel two of the .56 ohm which would yield .28 ohms at 24 watts. Also fine. 

[Dan Skye]

Larry gates vintage AR eBay store ,the best there is

[RoyC]

3 hours ago, Brad1234 said:

I saw those when searching for them online, but is 12 watts ok when the restoration doc calls for 20 watts?  

Brad,

When we were finalizing the restoration  guide, there was disagreement as to whether the resistor discussion should even be included. Ken Kantor's opinion was to simply use electrolytic capacitors if you want the best representation of the original sound.

The fact of the matter is that modern electrolytic capacitors behave more like AR's original AR-3a caps (all iterations) with respect to ESR. On the other hand, modern film caps will work very well in the 3a without the addition of fixed resistance given the resistance characteristics and relatively loose tolerances of the variable level controls.

For those people who added the extra resistors early on, don't worry about it. They are not making a significant "difference" one way or the other.

It should be noted that AR stopped using the nichrome type of .5 ohm resistor in the mid circuit sometime after cabinet serial number 80,000. It was replaced with an ordinary 5 watt (later, 10 watt) .5 ohm sandcast resistor in 1974. Inductance is not an issue worthy of concern.

Roy

PS Dan Skye, I do much work for Larry Lagace/Vintage AR. He does not sell resistors, nor would he recommend them in this case.

[Brad1234]

Thanks Roy!  I remember reading about the resistors not really being needed in another forum somewhere, that makes my rebuild job a little easier!  I have also worked with Larry at Vintage AR to get newly rebuilt tweeters for my AR 3a's, they sound fantastic!  I also got some of the Vintage AR woofer dope and doped my KLH Model 6 woofers, worked perfectly!  Highly recommend Vintage AR. 

[RoyC]

On 2/7/2022 at 9:33 AM, Brad1234 said:

Thanks Roy!  I remember reading about the resistors not really being needed in another forum somewhere, that makes my rebuild job a little easier!  I have also worked with Larry at Vintage AR to get newly rebuilt tweeters for my AR 3a's, they sound fantastic!  I also got some of the Vintage AR woofer dope and doped my KLH Model 6 woofers, worked perfectly!  Highly recommend Vintage AR.

Glad the tweeters are working out, Brad.

Forum members are welcome to contact me directly regarding tweeter/midrange/woofer repair and surround sealant. 😉

Roy

[Brad1234]

Just finished my restoration of my AR 3a's and playing them to "burn in" the new caps some, if that is really a thing. They sound much better with the new caps!  I had a quick dumb question though, I just noticed the nichrome wire resistor in the schematic after I have already closed up the speakers, was I supposed to test that and make sure it is still in spec?  I didnt see anything about checking it in the manual. I'm hoping its one of those resistors that works fine or not at all?  Just not sure if I should have checked it or looked at replacing it along w the caps?

[Dan Skye]

Beautiful work it’s so nice to see these exceptional speakers restored for future generations to appreciate as do we. I think what type of insulation did you put in the AR three cabinets? Did you put the old scratchy stuff back in or use something new?

[Brad1234]

I used all of the original fiberglass insulation, and added a little more just to account for volume of old capacitor box I removed. U have to wear long sleeves and gloves and a mask when dealing with the insulation or yes it does stab you all over and cause itching. I was working with it in direct sunlight and u could see the fibers flying all around. The fiberglass insulation gives the best sound, so its worth it. 

[Dan Skye]

 

19 minutes ago, Brad1234 said:

I used all of the original fiberglass insulation, and added a little more just to account for volume of old capacitor box I removed. U have to wear long sleeves and gloves and a mask when dealing with the insulation or yes it does stab you all over and cause itching. I was working with it in direct sunlight and u could see the fibers flying all around. The fiberglass insulation gives the best sound, so its worth it. 

Another thing that comes to mind is I think that nasty fiberglass is the culprit that damages the potentiometers and probably can make its way into the spiderweb around the back of the woofer .
 Nonetheless I have always stuck with the original insulation as well. I’ve restored many but I’m not as good as you by a long shot, you do beautiful work!

[Brad1234]

Thanks Dan! I worked really hard on this recap because I wanted to keep the changes in the cabinet to the bare minimum, so just used screw down ziptie brackets and silicone glue to hold the caps. 
 

I just wish I had checked that single resistor in the cabinet just to ensure it is still functioning in spec. Not sure if that would really make a sound difference anyway. 

[RoyC]

6 hours ago, Brad1234 said:

I just noticed the nichrome wire resistor in the schematic after I have already closed up the speakers, was I supposed to test that and make sure it is still in spec? 

 

1 hour ago, Brad1234 said:

I just wish I had checked that single resistor in the cabinet just to ensure it is still functioning in spec. Not sure if that would really make a sound difference anyway. 

Nice work. Don't worry about the nichrome resistor, Brad. In all the years I have been repairing and restoring 3a's I have never found one to be out of spec or bad.

A few years ago I did trace a non-functional mid to a corroded rivet, which connects the resistor to the rest of the circuit. Even then, the resistor itself measured perfectly when I removed it to correct the problem.

Roy

[Brad1234]

Thanks Roy!  I figured those resistors would be fine but just wanted to check. 

[bjmsam]

Echoing feedback posted over the past fifteen years, the guide is terrific and most appreciated!  I am preparing to dig into my pair which Dad bought new in the late 60s (serial numbers 06052 and 06064).  I am comfortable with NPEs (recently employed with success in my center channel project)...

On 10/15/2009 at 10:53 AM, JKent said:

The originals were non-polarized electrolytics and therefore cheap NPEs should work just fine

On 2/6/2022 at 11:00 PM, RoyC said:

Ken Kantor's opinion was to simply use electrolytic capacitors if you want the best representation of the original sound.

The fact of the matter is that modern electrolytic capacitors behave more like AR's original AR-3a caps (all iterations) with respect to ESR.

...but what are the early caps, exactly?  The guide seems somewhat ambiguous on this point:

Quote

The early crossover used a physically large, dual 150/50-μF woofer/mid-range capacitor and a separate 6-μF hi-range capacitor. The later crossover used individual non-polarized electrolytic capacitors encapsulated in aluminum cans.

On 10/19/2009 at 7:22 PM, Tekker said:

I have the original block caps and I don't believe they're electrolytics.

 

Also, the guide states:

Quote

Very early cabinets used a 1.88-mH AR #7 woofer inductor, but that was changed to a 2.85-mH AR-#9 coil to correct a slight “bump” in the speaker’s upper woofer range power output.

Since my woofers have cloth surrounds, the #7 inductor should not be replaced with a #9 coil, correct?

On 2/9/2011 at 3:21 AM, RoyC said:

-Cloth surround woofers and very early foam surround 3a woofers were at the lower end of the 18 hz+/- 15% fs specification, and the later, foam surround versions were at the higher end.

-There are response differences between the two types of woofers, which is the most likely reason for the change from #7 (1.88mh) to #9 (2.85mh) woofer inductor.

 

Sure glad I saw this - thank you!  Perhaps the guide should be updated for those not poring over every post?

On 9/23/2020 at 4:46 AM, roundcubenine said:

The AR-3a guide mentions using Permatex High Tack Gasket Sealant to reseal the fabric woofers, but I heard some complaints about this stuff, so I just bit the bullet and ordered the good stuff from Vintage-AR on eBay. It's about double the cost, but a lot cheaper than ruined woofers!

On 9/23/2020 at 2:57 PM, JKent said:

Good call! That recommendation to use Permatex slipped into the Guide before it was thoroughly tested over time and it turns out the stuff eventually gets stiff and ruins the surround. RoyC, an author of the Guide cooked up the stuff sold by Vintage AR and it's authentic to the original goo.

 

[Dan Skye]

Food luck,pulling for you!

Among the greatest speakers ever made IMHO

I still use a pair of 3 as my  main studio monitors as a professional engineer. They sound so natural and open. Amazing low end too

[bjmsam]

Thank you!  I agree and am thankful to have had the privilege of literally growing up with this pair.  After 54 years of continuous use, they still sound terrific and are most deserving of my attention.  CSP is a treasure!

 

[Brad1234]

I recapped my very early model AR 3a's about 6 weeks ago and they broken in nicely!  The hardest part was restoring the pots within the cabinet to avoid unsoldering them, but they were badly corroded and needed cleaning and greasing to work well again. I just ziptied my Jantzen Crosscaps to screw down plastic brackets. Night and day difference from the old brick type capacitors that were in there. Good luck and take your time!  

[genek]

16 hours ago, bjmsam said:

...but what are the early caps, exactly?  The guide seems somewhat ambiguous on this point:

I haven't ever cut one open, but the wax block caps were most likely stacked paper capacitors, layers of foil separated by waxed or oil impregnated paper, or layers of paper waxed on one face with foil bonded to the other.

[RoyC]

Attached is photo of the innards of a block cap. This one was used in an AR-5 crossover.

Roy

[bjmsam]

Thank you!  Very interesting.  So AR replaced those wax-paper-impregnated caps with NPE caps of equivalent capacitance (but presumably different Equivalent Series Resistance, Dissipation Factor, Dielectric Absorption, charge migration, etc.) with no other changes to the crossover network than one inductor that most likely was to accommodate a different woofer driver?

I do not have a way to measure caps like @Carlspeak did in the HERE'S WHY YOU SHOULD REPLACE THOSE OLD 3A CAPACITORS thread as I have only an LCR tester (and a TC1 tester that does not always show ESR) but will use REW with a calibrated UMIK-1 microphone to measure speaker output (in my room) before and after as @genek requested in that thread.

[genek]

If we could see a cross-section of the cap, it would probably be stacks that are folded over to fit into the box. We'd probably have to peel layers off to see whether they're separate sheets of foil and paper or paper with foil on one face. But from the small dents I see at the folds, I'm leaning toward paper with foil.

[RoyC]

2 hours ago, genek said:

I'm leaning toward paper with foil.

You're correct, Gene...The box contained three oily smelling impregnated paper and foil rolls. The roll in the foreground was peeled through several layers, and you can see some of the foil at the bottom. This was the 72/24uf AR-5 dual capacitor. The 50/150uf AR-3a dual capacitor is just bigger.

Roy