AR-5 Acquisition and Refurb

[MikeD]

New to the forum and have just acquired a pair of AR-5s and begun to restore them.  Foam surrounds are coming, and I plan to install the HiVi Q1R tweeters, as one of the originals are damaged and not working at all.  I have seen conflicting advice on these - should I use a 0.05mH coil or 0.1mH coil?

The serial numbers are K 18576 and K 17982.  There are no dates on the woofers, and the dates on the tweeters are Feb 9 1971 and Dec 31 1970.  I do not plan to pull the mids as they seem to be working fine.  I will be cleaning/refurbishing the pots.  They mostly work but are clearly dirty.  

It is clear that these AR5s have been opened previously.  The fill is mixed bag:  some fabric, some fiberglass and some chunks of foam.  Each weighed in at 22oz. There are newer white foam speaker "seals" instead of the black gunk that I have read about between the speaker frame and the cabinet.  Interestingly, one of the woofers was wired in reverse: one was blue to positive, red to negative and the other was opposite.   Any reason to think this was intentional?  Also, one of the woofers has the black sealant around the magnet.  Wondering why. 

I don't have a device to test the caps but I'm going to assume that after 50 years they should be replaced.   The layout looks original, but my question is why are there two capacitors isolated in a box, and the third on the crossover board?  I've seen pictures on this site where the 72µF and 24µF caps are exposed.  Do I need to keep the box layout?  I have not yet opened either one.   Also, how close must the values be to the originals?  I can't seem to locate a 72µF, (I see 68 and 75), but have found 24µF and 4µF on partsexpress.com.

Any real reason to replace the crossover coils?  Again, my testing ability is limited.

The wealth of knowledge on this site is amazing.  I am an amateur but can handle a schematic and a soldering iron well enough.  I am so looking forward to pairing these with my Dynaco ST70 amp (dead-stock original but I will be refreshing it as well) and not sure yet about a preamp.  I currently have a NAD 1600, not exactly period vintage but it works.  May go with something like a Dynaco PAS 2 or 3, however I would really like to keep my remote!  

I've owned Large Advents since 1977 and will be moving these once the AR5s are good-to-go.  My listening habits have changed somewhat over the years.

 

[Aadams]

You have a nice pair of unmolested 5s. 

Have you read the AR 3a restoration guide?  It will answer many of your questions.

JIC originality in both appearance and performance is important to you, are you aware your original tweeters can be rebuilt as long as the bodies are intact?

RE the pots: Consensus these days is replace with lpads or new style potentiometers.  As a long time pot hold out.  I can vouch, Lpads are better.

When you reseal the speakers use gasket tape, especially on the tweeters and mids, if you remove them for some reason.

AR 5 cabs should be stuffed with approx 22oz of fiberglass. Any other material is an experiment.

I have no idea why the duct seal is around the woofer magnet unless to stop a vibration or rattle.

 

1 hour ago, MikeD said:

Any real reason to replace the crossover coils?  Again, my testing ability is limited.

Unless they are damaged the answer is no. 

Adams

 

 

 

[JKent]

Welcome Mike!

Very nice find. Aadams answered most of your questions but I'll try to fill in some gaps 😉

1. Not sure about the tweeter coil. Roy is the expert on that. But I would suggest asking Chris or Roy about restoring BOTH original tweets.
2. The fabric you find inside may be the Kimpac. Save it if it is intact or you can replace it. There are options--ask if interested.
3. Some AR woofers were marked wrong. Use a battery to check your woofer's polarity and then be sure to connect them red to positive on both. You do not want out-of-phase woofers--there will be no bass. http://www.troelsgravesen.dk/polarity.htm
4. You do not need the "box". Just replace 3 individual caps. 75uF is certainly close enough to 72. Back then the tolerance on caps was +75%/-25%. If you are OCD like some of us you can use 68 + 4 in parallel.

Some thoughts on the preamp: I really like updatemydynaco.com and its sister site akitika.com. Dan Joffee makes very nice kits with excellent instructions and tech support. If you want a vintage "feel" that goes with your dynaco, look at the Akitika PR-102. Looks kinda vintage and has a remote https://www.akitika.com/PR102.html

If you aren't using a phono you could buy a vintage AR-SRC to use as a remote-control preamp. Or pair it with whatever preamp you choose. I have a spare AR-SRC so if you're interested in buying it send a PM (sorry for the sales pitch)

Kent

[MikeD]

Originality of sound is important, yes, and I would like to maintain close-to-original cosmetics as well.  I will be purchasing the 18 count lambswool linen and the reproduction emblems.  The walmut cabinets are in mostly excellent shape.  However, I am less concerned about the internal look of the tweeters, but will probably keep the originals in case that is important to somebody someday. Or I may sell them to defray some of the restoration costs.

Yes, I have read the AR3a restoration guide - fantastic information.  My questions are outside of that excellent write-up as far as I can tell.   In fact, that write-up seemed to favor the pots over Lpads.  I have yet to pull and inspect them and may have to replace them once I have a look.   With Lpads, you must add additional resistance, correct?  Do these values change with the AR5 compared to the AR3a references in the guide?   

Here is a summary of my remaining questions:

• Regarding the HiVi Q1R tweeters, I have seen conflicting coil advice on this site - should I use a 0.05mH coil or 0.1mH coil?
• The woofers were wired oppositely - one was red wire to positive, the other was blue wire to positive.    Any reason to think this was intentional?   
• Is there any significance to the box housing for the two larger capacitors?  I have not opened one yet and maybe the answer will be more clear when I do open it up.
• How closely do I need to match the 72µF cap?  Since I can't find one, should I use a 50 and a 22 together, or just go with a 68 or 75?
• Finally, my ears are 63 years old and never really were at the audiophile level anyway.  Will the construction or brand of capacitors really make a difference?

Thanks!

[JKent]

A couple of things:

1. Rebuilding the tweeters is not just for appearance. The Hi-Vi tweets are very good and most people are happy with them but they don't match the dispersion of the originals.
2. L-pads are better. The restoration guide was written a while back and some things change as we learn more. Roy is one of the authors of the guide and he uses L-pads exclusively.
3. Check your woofer polarity as I said in previous post
4. throw the wax (box) capacitor away
5. 75 is OK. 50 + 22 is OK
6. Brand makes little difference. Parts Express capacitors (Dayton) are good. Use film for low values, Non-polar electrolytic for high values

[MikeD]

Great - thanks to both of you for the information. 

So how do I pursue having the tweeters rebuilt?  I know I read somewhere in this site, probably older information, that they couldn't be rebuilt or at least not to match the original sound.  Again, I am skeptical that my ears are sensitive enough to appreciate the differences.  And i'd rather save some bucks for a suitable preamp, if I decide the NAD1600 isn't right for the setup.  I still have about $200 to spend on revamping the ST70, but I have solid-state ST120 I am using in the interim. 

The film vs. NPE statement was very helpful.  I'm guessing the only "low-value" cap would be the 4µF.

I will look more into Lpads based on your advice.  I have read so much from this site that my eyes are beginning to roll back a bit.  GREAT source for an amateur like me.   

 

[MikeD]

FYI, I just checked the polarity on both woofers and they are marked correctly.  So one was definitely wired backwards.  I measured 6.4 ohms for each, BTW.  Sound correct? 

[JKent]

RoyC rebuilds them. Send him a PM: https://community.classicspeakerpages.net/profile/101150-royc/ I put his rebuilds in some 3a's I restored for another member but my own 3a's have Hi-Vi.

Chris also rebuilds them https://community.classicspeakerpages.net/profile/179217-chris1this1/

Then decide if you want to spend the dough. The Hi-Vis are cheaper than the rebuilds and they do sound fine.

Definitely film for the 4uF. You could go either way on the 24 but NPE is probably a better choice. The real advantage to film is they last "forever" while NPEs will eventually drift or leak (but not in your lifetime or mine).

The NAD is a nice preamp. If it were me, I'd keep it. If you need Owner or Service manuals, here's a free download: https://www.hifiengine.com/manual_library/nad/1600.shtml

If your woofers are marked correctly, wiring one backwards was definitely wrong and the bass would be nil because the 2 woofers were working against each other. 6.4 DCR sounds right to me.

[Aadams]

38 minutes ago, MikeD said:

Again, I am skeptical that my ears are sensitive enough to appreciate the differences. 

If you can hear to 8k there is a difference.   And, it depends on source material as well as your listening habits.  RoyC is the only person I know of that can attest to a/b comparison.

Adams

[MikeD]

Y'all are great! 

So I lifted one of the capacitor boxes.  Feels like a block of wax.   ???

Probably going to stick with the HiVi's.   Hear above 8K?  I can't even hear my wife anymore.     My source material is mostly choral, classical and classic jazz.  I have a big collection of Mosaic Jazz box sets.   So my remaining question is the coil size for the HiVI's.  Seems I saw 0.05mH in reference to the AR3a and 0.10mH for the AR5.  Just trying to confirm.  I have NO IDEA what the impact of one over the other would be.  To be honest, I don't even fully understand the function of the coil.

Thanks for the affirmation of the NAD 1600.  There are SO many opinions out there about component matching and it is mostly beyond me.  I can hear the tube amp difference - or at least I could 10+ years ago which was the last time I used the ST70.  I shut it down because it is all original and I had read that bad things can happen with some of the older components, especially the selenium rectifier.  So I will modernize it a bit, but not sure which path I will take.  Leaning toward the VTA70 route.     

I am really excited about these AR5s!

[ar_pro]

Unmodified AR-5 speakers are very desirable, and my inclination would be to keep them as close to that condition as possible, and have the tweeters rebuilt.

It's not simply about frequency extension, the dispersion characteristic of the Classic Era tweeters had a lot to do with their success. 

The NAD preamp would be a nice combination with a refreshed Stereo 70. Are you doing a stock restoration?

[MikeD]

Pardon  - I see that you mention the "wax" capacitor box above.  Will discard and get individual capacitor replacements. 

Are the metalized polypropylene capacitors considered "film" capacitors?  The word "film" is not used at partsexpress except for the (expensive) Film and Foil caps.  Also, they do not show a 24µF in the NPE style.  The closest is 22, then their offering jumps to 33.  So is it better to get the Metalized poly in the correct 24 size, or get the NPE 22?   In general, when size can't be matched, should you get something a little lower or a little higher?

[Aadams]

19 minutes ago, MikeD said:

My source material is mostly choral, classical and classic jazz.  I have a big collection of Mosaic Jazz box sets. 

Which is exactly the kind of material for which the AR5 was built.  The original tweeter is the only tweeter that uniformly extends the power response of the AR5/3a domed mid into the next octave. which is a big deal with live recordings or large classical ensembles.  The HIVis are more of an on axis tweeter and work fine for studio recordings.

Adams

[MikeD]

ar_pro - I am leaning toward the VTA70 classic mod (tubes4hifi), but am VERY open to suggestion.  A lot of different opinions out there.  

I will find out the cost of the tweeter rebuild before I decide on the final solution.  I'm not in a big hurry.

 

[ar_pro]

I really like the Stereo 70 in stock condition, but with a diode replacement for the selenium rectifier. 

Years ago, I did a conservative modernization of a rusty ST-70 from the late '50s that included re-plating the chassis, and powder-coating the cage and transformer housings. The original phenolic board was replaced with a very nice fiberglass type that was identical, so that I could keep the 7199 driver tubes. Everything was wired exactly according to the manual, but with teflon wire, modern sockets & switches and tighter-spec resistors and caps. As I recall, noise and hum were very low after the rebuild, and there was plenty of punch for a 35 watt/channel amplifier. 

There are many well-regarded mods for the ST-70, and all sorts of upgraded parts available, so there are lots of options.

[JKent]

2 hours ago, MikeD said:

Are the metalized polypropylene capacitors considered "film" capacitors?  The word "film" is not used at partsexpress except for the (expensive) Film and Foil caps.  Also, they do not show a 24µF in the NPE style.  The closest is 22, then their offering jumps to 33.  So is it better to get the Metalized poly in the correct 24 size, or get the NPE 22?   In general, when size can't be matched, should you get something a little lower or a little higher?

Sorry. Yes. Poly is film. You can get the 22uF NPE and add a 2.2uF NPE OR a 2uF film to reach ~24uF. 22 + 2.2 NPE is probably the way to go.

Regarding your amp, I believe that http://www.tubes4hifi.com/bob.htm is well regarded. Bob Latino seems to have a following.

This place has lots of parts: https://www.dynakitparts.com

[DavidR]

I have a Bob Latino ST-120 tube amp. Bob is a great guy and will always provide superb assistance.

I drive AR10Pi and AR91 in pentode mode without issues. I've even driven my AR90's.

 

[MikeD]

Thanks for all the responses.  I'm learning a lot.

DavidR,  the ST120 is really nice, but I wonder if I need that much power in my small listening room (13x14).  An ST70 in essentially stock mode (VTA70 or not) should be plenty to drive the AR5s, correct?  It was all my Advents (and my ears) could handle back in the day.  Also, in your opinion, is the pentode/triode switching nice to have or just fluff?  I'm curious what the difference in sound would be, but after that I wonder if would I care or ever switch back and forth. 

[DavidR]

I like having the triode and pentode mode but I'm usually in pentode mode because of what I'm driving.

The ST120 is 35 watts per channel in Triode. Not sure about the ST70. You should ask Bob. Join the website and send him a PM.

Go to the website:   https://dynacotubeaudio.forumotion.com/

[MikeD]

On 8/9/2020 at 3:09 PM, DavidR said:

I like having the triode and pentode mode but I'm usually in pentode mode because of what I'm driving.

The ST120 is 35 watts per channel in Triode. Not sure about the ST70. You should ask Bob. Join the website and send him a PM.

Go to the website:   https://dynacotubeaudio.forumotion.com/

Thanks, DavidR.   I've been a member of that forum for many years, but haven't been out there in quite some time.  I mothballed the ST70 some 10+ years ago.  The AR-5 acquisition has rejuvenated my interest in building a nice vintage system.  So  I guess I am interested in the (switchable pentode/triode) novelty on the VTA70 build, but have no idea what I'll like best.  And while I plan to use the AR-5s when they are ready, I don't know how efficient they are or aren't.  It is shaping up to be a fun and rewarding project.  M

[frankmarsi]

MikeD & JKent.

SEE LINK:

 

[DavidR]

Who's this Frank Marsi guy ?

[frankmarsi]

23 hours ago, DavidR said:

Who's this Frank Marsi guy ?

Not sure but, he's got a whole bunch of stereo stories.

And I hear that in about 6 months or so he will celebrating his 'Golden Jubilee', for a 50th anniversary of using and listening to AR speakers.

 

[AR surround]

On 8/11/2020 at 11:10 PM, DavidR said:

Who's this Frank Marsi guy ?

Beware as he's obviously lurking...like many of us.

On 8/12/2020 at 1:17 AM, frankmarsi said:

Not sure but, he's got a whole bunch of stereo stories.

And I hear that in about 6 months or so he will celebrating his 'Golden Jubilee', for a 50th anniversary of using and listening to AR speakers.

 

Geez Frank, you're old!  I won't have my Golden Jubilee until June 2022.  And yes, they were my beloved AR5's which fortunately remain in the family.

[frankmarsi]

10 hours ago, AR surround said:

Beware as he's obviously lurking...like many of us.

Geez Frank, you're old!  I won't have my Golden Jubilee until June 2022.  And yes, they were my beloved AR5's which fortunately remain in the family.

 

I'm seasoned and I've had more time to have fun everyday in doing whatever I do my whole life through.

Additionally, I've had more time listening to AR speakers than I've been on this site and I've been here since 2004.

I'm no johnny-come-lately like some folks who only have discovered these speakers in the last 10 or 15 years. I bought my AR-3a's brand new in '71.

As I've stated, I learned about room placement, input set-up, and system-building before I purchased my AR's 50 years ago.

I wear medals on my chest and stripes on my sleeves.

From what you've stated, it seems you're not far behind.