My "new" AR 3a

[Guest ARtwox]

Just got a pair of early 3a:s - the woofers need refoaming etc.

All drivers are working (playing) on both speakers.

I measured the resistance over the terminals; one was 3.5 Ohms, but the other was approx. 26.5 Ohms...anybody has a clue what might be going on here?

Thanks!

[Carlspeak]

>Just got a pair of early 3a:s - the woofers need refoaming

>etc.

>All drivers are working (playing) on both speakers.

>I measured the resistance over the terminals; one was 3.5

>Ohms, but the other was approx. 26.5 Ohms...anybody has a clue

>what might be going on here?

>Thanks!

>

What you are measuring is the DC resistance across the woofer coil and VC. The high resistance you got is symptomatic of a potential VC issue. The 3.5 ohms is about right.

Are you sure that particular woofer plays okay?

Suggest you play music thru it some more, listen carefully and measure it again after disconnecting it from your amp/receiver.

It's all about the music

Carl

Carl's Custom Loudspeaker

[dynaco_dan]

Hi there;

If you are measuring at the terminal connections, you are only testing the woofer circuit, not the mid or tweeter.

[Guest ARtwox]

>>Just got a pair of early 3a:s - the woofers need

>refoaming

>>etc.

>>All drivers are working (playing) on both speakers.

>>I measured the resistance over the terminals; one was 3.5

>>Ohms, but the other was approx. 26.5 Ohms...anybody has a

>clue

>>what might be going on here?

>>Thanks!

>>

>

>What you are measuring is the DC resistance across the woofer

>coil and VC. The high resistance you got is symptomatic of a

>potential VC issue. The 3.5 ohms is about right.

>Are you sure that particular woofer plays okay?

>Suggest you play music thru it some more, listen carefully and

>measure it again after disconnecting it from your

>amp/receiver.

>

>It's all about the music

>

>Carl

>Carl's Custom Loudspeaker

Hi Carl,

Thanks for your reply, but being a tech dummy, I have no clue what VC stands for. When you say "Are you sure that particular woofer plays okay?", I really don't know what okay would be like here...it plays.

The condition these speakers are in, unfortunately doesn't allow me to crank up the volume too much at all (completely disintegrating surrounds with lots of holes in them - they seem to have been patched up with gauze and "all sorts of stuff" on a number of occasions.

Getting these sorted is very much a project over time, and my idea was to sort the technical bits first and then (if I like what I hear ), I'd seriously consider having the woodwork sorted out professionally.

BTW; the serial number of these are 5XXX, if that's any help (?).

Peter

[Carlspeak]

Peter.

VC stands for voice coil. If it's damaged or partially hung up in any way it could affect the ohms reading.

Try playing the speaker laying on its back. In that way there won't be as much stress on the obviously bad surround. It will also help center the VC easier. If you hear any rubbing, then you may have a VC problem.

You can also try genltly pushing down on the dust cap and listening for rubbing sounds. You should hear nothing if the VC is centered properly.

You will have to remove the woofer eventually anyway to refoam it and then check the DC resistance again and also check the internal wiring for any obvious signs of toasting from very high current.

It's all about the music

Carl

Carl's Custom Loudspeakers

[Guest ARtwox]

Hi Carl,

I played them on very low volume for a while, left them for some time, and measured the resistance again...they're both roughly the same now...go figure.

Much to my dismay though, I found that one of the tweeters were not working, irrespective om me turning and fiddling with the tweeter pot.

Can this be repaired?

Peter

[Carlspeak]

>Hi Carl,

>

>I played them on very low volume for a while, left them for

>some time, and measured the resistance again...they're both

>roughly the same now...go figure.

I hope that means they are both about 3.5 ohms.

>Much to my dismay though, I found that one of the tweeters

>were not working, irrespective om me turning and fiddling with

>the tweeter pot.

>

>Can this be repaired?

More often than not, the tweeter rheostat is the problem - not the tweeter itself.

Remove the woofer and stuffing and pry off the wire that holds the tweeter rheostat together and inspect the wiper and wiper plate. You will probably find they are corroded. Clean it up as best you can (many posts here regarding cleaning pots), re-assemble and test it.

>

>Peter

It's all about the music

Carl

Carl's Custom Loudspeakers

[Guest ARtwox]

I removed all drivers, to find that the tweeter indeed is busted.

Can this be repaired?

I know it's a long shot, but I recall reading somewhere on the web about a guy who had a shot 3a tweeter and performed surgery on it - successfully so it seems.

I just can't seem to remember where I read it (:-(

Any experience with this type of surgery?

Thanks!

Peter

[RoyC]

>I removed all drivers, to find that the tweeter indeed is

>busted.

>Can this be repaired?

Peter,

The answer is no, unless you can determine if either or both of the hair-like voice coil leads are disconnected from the tinsel lead under the electrical tape. That is the only thing that can be repaired.

Roy

[Carlspeak]

>I removed all drivers, to find that the tweeter indeed is

>busted.

>Can this be repaired?

>I know it's a long shot, but I recall reading somewhere on the

>web about a guy who had a shot 3a tweeter and performed

>surgery on it - successfully so it seems.

>I just can't seem to remember where I read it (:-(

>Any experience with this type of surgery?

Sorry, I just pull teeth - don't perform brain surgery (so to speak)

I agree with Roy on this one.

It's all about the music

Carl

Carl's Custom Loudspeakers

[Guest ARtwox]

Hi,

Thanks for all the feedback on this.

I was thinking; is the tweeter used in AR 5 the same as the one used in the 3A?

Or what about the one used in the 2ax?

Many thanks!!!

[KlausDK]

Hi Peter

In principal the 5 and 2ax tweeters are the same as the AR-3a, but they differ in the impedance: 3a being 4 Ohm, whereas the 5 and 2ax are 8 Ohm, and they are therefore not interchangeable with the 3a system.

BRgds Klaus

[Guest ARtwox]

Hello,

OK, and there doesn't appear to be any real supply of original used replacement tweeters either, so what can one do?

I'd like to retain the original "sound signature" of the 3a - what would be the best replacement option available...any ideas?

Thanks!

Peter

[dynaco_dan]

Hi Peter;

Keep your eyes open on ebay.

Be cautious with the sellers description though.

If they claim the tweeter came from an AR-3A or LST you might believe it.

They sometimes claim they will fit AR-2AX's, LST/2's, AR-3's, AR-3A's, AR-5's and maybe others, as well.

If they post DCR of maybe around 3 you, are safe.

If the DCR is 5.75 or in that neighbourhood, it is an 8 ohm tweeter.

There is usually one or two on auction at least once a month or more often.

The packaging of the tweeter is most critical as it has a very vulnerable small dome.

[RoyC]

Peter,

There are two routes you can take:

1)Replace the original tweeter with another.

2)Use a modern tweeter such as the AB Tech "AR replacement" driver with a slight crossover modification (namely a small inductor in parallel with the new tweeter). If you go this route you should replace both tweeters. The overall character will be very close to the original, with an added bonus of more useful tweeter level control positions.

Much has been discussed about the second option elsewhere in the forum. Based on recent experimentation, I believe it is not only a viable solution, but rapidly becoming a necessary one, as the old dome suspensions lose their integrity and original response characteristics. The attached photo shows the disintegrating suspension and damping foam of an original 3a (1971 era) tweeter.

I have a spare original 3a tweeter available. If you are interested, contact me through the forum email feature.

Roy

[Guest Andy99]

Hi Roy and all,

I have two Ar 3a speakers, and I'm approacing the repairing activitieas for them.

I've refoamed both the woofer with a good result, and I'm trying to find out the best solution about the tweeters and the crossover filters.

After a long research, I would believe that you and this forum

can provide to me lots of good advices.

Tweeters:

Because one original tweeter has broken I have to change both.

After a long research I've found ABtech tweeters and it seems from your forum that they sound good, and don't change to much the global original Ar3a sound. Is it correct?

In some other sites there is also a very well organised "Vintage AR parts and service" that provides Ar 3a tweeters too. Have you /some one tested them too?

For the AB tech tweeters there are no information, also from ABTech contanct point.

Are these tweeter full electrically compatible with the original crossover? Is the Impedence about 4 ohms (consider that my measurement with dc tester of the original good one were about 3.6 ohms), have they the same inductance so I can keep the same filter (just 6mfd capacitor and the 15 ohms potentiometer)?

You advice an inductance in parallel to the tweeter, which could be the value? The reason for it is to decrease some high freq. efficency or because you have measured them and they need a freq. correction?

Maybe are they ferrofluid cooled? Is the dome in nylon, silk or what, in general is the dome material soft?

Cross over:

Could you please advice me about the capacitors? The original one for the tweeter has shifted from 6 to about 8 mfd, that I beleieva was the reason for damaging the original tweeter.

Those capacitors are not available neither in Italy (I'm from Rome) nor in Europe, therefore I have to buy them too.

Have you tested some specific capacitors, e.g. only the 6mfd one can be poliester (I mean not electrolitic), while the otehr two can be electrolitics? For your opinion 100Volts voltage for the capacitors can be enaugh for driving the speakers without risks?

I hope that you can help me and I thank you very much in advance for the patient in reading so long comments (with my terribly bad english/american.. from Italy!)

Thank you,

Andrea.

[RoyC]

Hi Andrea,

The AB Tech tweeter (www.abtechservices.com) is a 4 ohm, 3/4" cloth dome, ferro fluid tweeter which is sold as an "AR replacement", and fits the 3a cabinet opening. The connection terminals are on the back, so you would have to make adjustments (including notches for the terminals in the cabinet hole) if your old tweeters are front-wired. The same tweeter is also sold by a reliable Ebay seller by the name of "Vintage AR".

It is obvious that your caps need to be replaced. There are a number of good sources for these in the US that ship internationally. (One of my favorite parts sellers is Madisound.com.) A 100v rating or higher will work fine, and film caps such as polypropylene or mylar are more durable and consistent than electrolytics.

Based on measurements by another forum member, Ken Kantor, and my own experimentation with Ken's findings, a parallel inductor across the AB Tech tweeter of around .07mh works pretty well with the original value (6uf) tweeter cap and the original pots. (To answer your question..the parallel inductor rolls the ABT tweeter's response off faster, resulting in a response more like the original tweeter.)

I personally prefer the sound when using a smaller inductor of .05mh in conjunction with an 8 ohm l-pad, instead of the original potentiometer. Added benefits to this arrangement are:

1) it replaces the typically troublesome pots, and

2) .05mh inductors and 8 ohm l-pads are parts that are easily purchased.

Also, adding between .5 to.8 ohms in series with the tweeter cap, and reversing the polarity of the ABT tweeter, seems to optimize the circuit in my opinion.

Feel free to send an email through the forum feature if I can be of further assistance.

Roy