The verdict is in...

[GraphicFX]

Upon dissection of the right speaker's sda driver, it is clearly stamped on the sticker on the back of the magnet; "SDA 2B" with a manufacturing date of March 3, 1990.

The model # is MW6511.

Using a "pin/blade" IC, with the older style cabs (38-1/2" tall), along with a manufacturing date of 1990, leaves me to believe they are SDA 2B studio's. The non studio version of these had the newer style cabs (39-1/2" tall) with cloth sides and real wood (advent style) bottom and tops.

Well, that clarifies that.
Although I hate to admit it, F1 nut was correct.

[vstarkwell]

Although I hate to admit it, F1 nut was correct.

He knows his stuff

[Kingman]

Although I hate to admit it, F1 nut was correct.

He knows his stuff

X 2!

[schwarcw]

Glad to hear that you are enjoying the Polks GFX.  I have been a Polk owner for 10 years.  F1 has provided me exceptional guidance, help and recommendations.  He knows his Polks!  My system sounds much better today based on F1's advice.

Now that you have the SDA fever, life will get better for you!  LOL!  Join the Polk Forum, a lot of good people and information about SDAs and the other fine Polk products are there.

Good luck!

[OldiesButGoodies]

Carl - you do this to annoy me!    I want to own SDAs some day and get the Polk fever. They are in the bucket list.

[GraphicFX]

Carl - you do this to annoy me!    I want to own SDAs some day and get the Polk fever. They are in the bucket list.

http://washingtondc.craigslist.org/nva/pts/4594556045.html

two pairs of sda's. One pair looks like 1c's the other a 2a or 2b.

$260 for each pair.

a short drive to DC. I'd jump on them if i didn't just get a pair.