AR-3a Drivers

[Guest postjob62]

Were the mid-driver and tweeter for the 3a the same throughout it's entire model run even though there were changes in the woofer? And, are either of these mid and HF drivers the same as any other AR drivers in that time period?

Also, were there only the two variations of the 12" woofer, generally distinguished as alnico/cloth surround--->ferrite/foam surround? Any fairly definitve idea when these changes took place, either by production time or serial #?

Thanks,

Ed

[tysontom]

>Were the mid-driver and tweeter for the 3a the same

>throughout it's entire model run even though there were

>changes in the woofer? And, are either of these mid and HF

>drivers the same as any other AR drivers in that time

>period?

>

>Also, were there only the two variations of the 12" woofer,

>generally distinguished as alnico/cloth

>surround--->ferrite/foam surround? Any fairly definitve idea

>when these changes took place, either by production time or

>serial #?

>

>Thanks,

Ed,

The 4-ohm midrange and the tweeter were *essentially* the same for all of the AR-3as throughout its life. In approximately 1975 AR changed the AR-3a rather significantly by doing away with the front-wired ("hard-wired") midrange and tweeter terminal strip, and went to the tab-connection, back-wired versions. This AR-3a version is also characterized by the velcro-attached grill, thicker grill material and the skimpy serial-number tag on the back-side of the speaker. I think this might have been the change in the woofer-midrange crossover frequency, but I am not certain of the time of this change. The 1-1/2-inch midrange drivers for this variety have the protective screen recessed rather than glued to the top of the top plate and the connections are, of course, from the back of the driver. The tweeters had two solder lugs on the front side of the driver, with a tab connection on the back for wiring. These tweeters were the same basic 3/4-inch, hard-dome versions, but the quality control by this time was declining. Some domes of this vintage were installed at an angle to the top plate.

The other speaker to share these 4-ohm drivers was the AR-LST. The AR-11 and the AR-10Pi shared the 1-1/2-inch back-wired midrange driver, but used a different tweeter. The woofers were largely the same, but there are different iterations which are discussed at length elsewhere in this discussion, see: "Evolution of and Replacements for the AR 11/12" Woofer."

--Tom Tyson

[Guest postjob62]

Tom,

Thanks much for your response. The purpose of my post is to make sure that restoration effort is put into the best possible candidate. I wasn't aware of this third late-production iteration, and it sounds like it is less desireable than others. Mine do have the skimpy back label, which is pre-printed 10/73 but of course could have been used any time after that. S/N is 85,140. Having said this, they appear to my less-than-knowledgeable eyes to have front-wired mid and HF drivers; there is a skinny copper lead under each piece of black electrical tape which goes to what looks to be the terminal strip you mention. The mid protective screen does not look to be recessed, but rather glued/attached from the front.

Not trusting my own conclusions, however, would you (and others) mind taking a look at the pic I have attached to make sure these are not the less-desireable units you reference?

Given my propensity to fairly loud classic rock and blues, I do think I would be better served by restoring a pair with the later style ceramic magnet woofer and foam surrounds.

Thanks,

Ed

622.txt

[Guest postjob62]

Whoops, forgot one more question: would these mids and tweeters appear to be interchangeable with all others in the production run except the late aberrations you mentioned?

Ed

[ninohernes]

>

>Given my propensity to fairly loud classic rock and blues, I

>do think I would be better served by restoring a pair with the

>later style ceramic magnet woofer and foam surrounds.

>

>Thanks,

>

>Ed

I tend to prefer the alnico woofer over the ceramic one. It is a really huge powerful magnet.

[tysontom]

>Tom,

>

>Thanks much for your response. The purpose of my post is to

>make sure that restoration effort is put into the best

>possible candidate. I wasn't aware of this third

>late-production iteration, and it sounds like it is less

>desireable than others. Mine do have the skimpy back label,

>which is pre-printed 10/73 but of course could have been used

>any time after that. S/N is 85,140. Having said this, they

>appear to my less-than-knowledgeable eyes to have front-wired

>mid and HF drivers; there is a skinny copper lead under each

>piece of black electrical tape which goes to what looks to be

>the terminal strip you mention. The mid protective screen does

>not look to be recessed, but rather glued/attached from the

>front.

>

>Not trusting my own conclusions, however, would you (and

>others) mind taking a look at the pic I have attached to make

>sure these are not the less-desireable units you reference?

>

>Given my propensity to fairly loud classic rock and blues, I

>do think I would be better served by restoring a pair with the

>later style ceramic magnet woofer and foam surrounds.

>

Ed,

You have late-production model of an "early" version AR-3a; that is, the midrange driver and tweeter are both "hard-wired" versions of the speaker, the grill panels were hot-melt-glued on and so forth, but they were probably produced in the Norwood factory, as evidenced by the small Norwood sticker. As you noted, the screen on the midrange is glued to the midrange top plate rather than recessed. The woofer you have is the first iteration 200003-0 woofer, a highly desirable and very compliant ceramic-ferrite woofer that should definitely be re-foamed and retained. It appears that the original surround is still intact -- something fairly rare these days -- but these thirty-year-old surrounds won't last much longer.

You should consider going in and refurbishing the level controls, observing closely the instructions we have posted on this site in many places, and you should replace the foam surrounds on each woofer with the correct, angled, 5/8-inch-diameter half-roll surround. You could at this time also refinish the oiled-walnut cabinets.

As for playing "fairly loud classic rock and blues," there is no reason that you could not use the AR-3a and its existing drivers for that purpose, so long as you don't "go over the top" and as long as you have sufficient amplifier power to prevent clipping. As a safeguard, you might consider fusing the speakers with the Bussman FNM 1-1/4-amp slow-blow fuse. This will usually protect the tweeters, but not always, against excessive power or clipping. Good luck on your project!

--Tom Tyson

[dynaco_dan]

>>Tom,

>>

>>Thanks much for your response. The purpose of my post is to

>>make sure that restoration effort is put into the best

>>possible candidate. I wasn't aware of this third

>>late-production iteration, and it sounds like it is less

>>desireable than others. Mine do have the skimpy back label,

>>which is pre-printed 10/73 but of course could have been

>used

>>any time after that. S/N is 85,140. Having said this, they

>>appear to my less-than-knowledgeable eyes to have

>front-wired

>>mid and HF drivers; there is a skinny copper lead under each

>>piece of black electrical tape which goes to what looks to

>be

>>the terminal strip you mention. The mid protective screen

>does

>>not look to be recessed, but rather glued/attached from the

>>front.

>>

>>Not trusting my own conclusions, however, would you (and

>>others) mind taking a look at the pic I have attached to

>make

>>sure these are not the less-desireable units you reference?

>>

>>Given my propensity to fairly loud classic rock and blues, I

>>do think I would be better served by restoring a pair with

>the

>>later style ceramic magnet woofer and foam surrounds.

>>

>

>Ed,

>

>You have late-production model of an "early" version AR-3a;

>that is, the midrange driver and tweeter are both "hard-wired"

>versions of the speaker, the grill panels were hot-melt-glued

>on and so forth, but they were probably produced in the

>Norwood factory, as evidenced by the small Norwood sticker.

>As you noted, the screen on the midrange is glued to the

>midrange top plate rather than recessed. The woofer you have

>is the first iteration 200003-0 woofer, a highly desirable and

>very compliant ceramic-ferrite woofer that should definitely

>be re-foamed and retained. It appears that the original

>surround is still intact -- something fairly rare these days

>-- but these thirty-year-old surrounds won't last much

>longer.

>

>You should consider going in and refurbishing the level

>controls, observing closely the instructions we have posted on

>this site in many places, and you should replace the foam

>surrounds on each woofer with the correct, angled,

>5/8-inch-diameter half-roll surround. You could at this time

>also refinish the oiled-walnut cabinets.

>

>As for playing "fairly loud classic rock and blues," there is

>no reason that you could not use the AR-3a and its existing

>drivers for that purpose, so long as you don't "go over the

>top" and as long as you have sufficient amplifier power to

>prevent clipping. As a safeguard, you might consider fusing

>the speakers with the Bussman FNM 1-1/4-amp slow-blow fuse.

>This will usually protect the tweeters, but not always,

>against excessive power or clipping. Good luck on your

>project!

>

>--Tom Tyson

Hi Ed

In the AR library there is a fusing information sheet for AR speakers from AR.

It lists most all of the AR classic speakers, and it also will show you the approximate power handling capabilities with their Bussman FNM recommended fuse.

There was also another brand, Littlefuse, which also listed an equivalent model and amp ratings.

I have an old Littlefuse catalog in my messy museum just out of my reach at this moment, but this also might be available as well.

Old electronic stores may have them still gathering dust on their shelves.

Note the small amperage ratings though.

AR was extremely generous with this data and they also, at that time, sold the fuses, and or, fuse holders, to their customers at their cost.

Unfortunately, I didn't buy cases of them as an investment back then, because they are difficult to find now and expensive.

They are difficult to find as in not here in Vancouver and the bases are as well.

As a side note, I have AR-LST's which have not the fuse block, but the fuse clips only soldered to the rear circuit boards.

I can only guess that they got them too hot, when they soldered them, to the circuit board, and they tend to break at the solder joint, they are not copper or brass.

I have been a little creative, duh, When I lost my speaker one day, I went to the rear of the cabinet, and the fuse had just barely not contacted the one end of the fuse clip.

I found that the other one broke later as well.

My solution was, I had spare fuse blocks, to drilled out the copper rivet fastening the clip to the fuse block with a small drill bit.

The clips are not considered solderable, perhaps chromes spring steel? Not to be re-soldered anyways, or re-drilled or Whitney punched larger.

That gave me 2 fuse clips to use, I then drilled a small pilot hole where the original soldered clip hole would be, removed the broken existing fuse clip, I then used a very small brass machine screw, lock washer and double locking brass nuts inside the enclosure to fasten the new clip into position.

Of course I used Deoxit on these parts also, over-kill I know, but.

The individual fuse blocks should not be of any concern to any one, as they only receive the heat from the fuse end caps.

Now back to the recommended fusing sheet.

Barring that you can't find these fuseholders, or fuses, an open type 1/4" x 1" fuseholder soldered inline, at perhaps the rear of the speaker enclosure, using fast blow fuses, starting at 1 amp fast blow will give you some sense of security from overload.

As another side note, for the AR component AS-103 speaker, as sold by Heathkit during AR's classic era.

Heath recommended, and supplied a chassis mounted fuseholder complete with o'ring seal for it's cap, I would suggest only an open type to allow the fuses to keep a little cooler.

They used a 3 amp fast blow fuse.

I can only assume that Heath and AR arrived at this particular rating, they were certainly less expensive for the mass market.

If you should go the 1 amp route, keep lots of spares on hand, they are only a few nickels each.

Also remember that the speakers are also over 25 years old, so they shouldn't be driven as hard as when they were new.

I rattle a lot.

Good luck.

[Guest postjob62]

Thanks to all for the valuable input on the 3a drivers. Following up on my original question, are either the 3a's tweeter or it's mids shared with any other AR speaker? The tweeters look like the post-1970 2ax tweeters, at least from the front. Not sure about the mid drivers.

Ed

[RoyC]

Hi Ed,

Some systems used 8 ohm drivers that appear identical to the 4 ohm AR-3a drivers.

The AR-5, LST-II and later AR-2ax all used an 8 ohm version of the AR-3a tweeter.

The AR-5 and LST-II used an 8 ohm version of the AR-3a midrange.

The 8 ohm versions shouldn't be used as drop in replacement drivers for the 3a. Tom mentioned the systems that used the AR-3a drivers in an earlier post in this thread.

Roy

[Guest postjob62]

Thanks Roy,

The instant I hit "post message" I realized I had suffered a brain lapse as regards the 3a being 4 ohms. Just hoping for an expanded source for drivers, I suppose.

Given the visual similarity of the tweeters, is there any part #, other identification, etc. on the 3/4" tweeters to distinguish between the 4 ohm 3a version and the 8 ohm 2ax version when buying them used and removed from the enclosure?

Regards,

Ed

[RoyC]

Unless I've missed something along the way, I believe it is impossible to tell the difference by looking at them.

The part #'s are as follows:

4 ohm mid is #1200010-1

8 ohm mid is #1200010-2

4 ohm tweeter is #1200011-1

8 ohm tweeter is #1200011-2

Unfortunately it is usually tough to find a part number on them.

The DC resistance of the 4 ohm drivers will measure close to 3 ohms and the 8 ohm versions will measure around 6 ohms.

There are not many 8 ohm mids floating around out there given the small number and lower sales volume of models containing it.

On the other hand the AR-3a 4 ohm mid was in service a long time and in a greater number of models. There are many more of these to be found.

The popularity of the AR-2ax has resulted in quite a few 8 ohm tweeters in the world of used AR parts. If you are looking for an AR-3a tweeter it is best to know where it is coming from or know what the DC resistance is before springing for it.

Roy

[dynaco_dan]

>Unless I've missed something along the way, I believe it is

>impossible to tell the difference by looking at them.

>

>The part #'s are as follows:

>4 ohm mid is #1200010-1

>8 ohm mid is #1200010-2

>4 ohm tweeter is #1200011-1

>8 ohm tweeter is #1200011-2

>

>Unfortunately it is usually tough to find a part number on

>them.

>

>The DC resistance of the 4 ohm drivers will measure close to 3

>ohms and the 8 ohm versions will measure around 6 ohms.

>

>There are not many 8 ohm mids floating around out there given

>the small number and lower sales volume of models containing

>it.

>On the other hand the AR-3a 4 ohm mid was in service a long

>time and in a greater number of models. There are many more of

>these to be found.

>

>The popularity of the AR-2ax has resulted in quite a few 8 ohm

>tweeters in the world of used AR parts. If you are looking for

>an AR-3a tweeter it is best to know where it is coming from or

>know what the DC resistance is before springing for it.

>

>Roy

Hi there

More great information from you as usual, Roy.

When I find my only 3/4" AR tweeter, with the power resistor hot glued on the rear of its magnet, I'll be able to add to this site.

My belief is that AR or their supplier produced 8 ohm tweeters and added a parallel resistor to make it 4 ohm, or by cutting one lead of the resistor it could be used as 8 ohm.

Not adding a resistor in series with a 4 ohm tweeter.

Engineering wise this would not be an appropriate method, tremendous loss of signal.

But the dollar talks louder some times.

If my memory serves me right, that tweeter had a red label, ( such as a replacement label ?)

I know I've seen an AR OEM sheet, stating a replacement 3/4" tweeter and listed all of the 4 and 8 ohm speakers models together, without notation of this resistor.

Possibly AR noticed this fact and later added an amendment, there must be a copy of this somewhere out there.

[Guest postjob62]

Roy,

I can't tell you how helpful that is to me. Thank you for taking the time to share the knowledge.

And while I'm at it, thanks to Tom, Steve F., johnnieo, and all the others whose knowledge and willigness to help make this forum such a great resource.

Ed

[frankmarsi]

Tom T., anyone? Can anyone out theresend me a schematic of the AR-LST tweeters. I'm replacing the out burnt ones with AB-Tech drivers and will speak after project is done, but in the mean time I'm lost!

Respectful to all AR people as I've been one since '72.

Frank Marsi

email: frankmarsi@verizon.net

[dynaco_dan]

>Tom T., anyone? Can anyone out theresend me a schematic of

>the AR-LST tweeters. I'm replacing the out burnt ones with

>AB-Tech drivers and will speak after project is done, but in

>the mean time I'm lost!

>Respectful to all AR people as I've been one since '72.

>Frank Marsi

> email: frankmarsi@verizon.net

Hi Frank;

Check out the AR library, there is a LST manual for download.

Good luck.