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A very interesting AR 3a find over on AK.


GD70
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59 minutes ago, GD70 said:

This is fascinating. Maybe someone here can shed some light on this gents find.

Glenn

http://audiokarma.org/forums/index.php?threads/a-trio-of-vintage-soldiers-or-this-never-happens-to-me.805394/

Thanks for the heads up, Glenn.

I would love to get a close look at the 3a's with the apparent LST parts. If original, we could be seeing an AR-10pi prototype.

Roy

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3 hours ago, RoyC said:

Thanks for the heads up, Glenn.

I would love to get a close look at the 3a's with the apparent LST parts. If original, we could be seeing an AR-10pi prototype.

Roy

That 3F has a plywood backing so an older box but yet the other 3a boxes are recent. Do you think it might be a DIY project? The driver cut outs for the mid and tweeter are really off base too on the 3F.

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18 hours ago, lakecat said:

That 3F has a plywood backing so an older box but yet the other 3a boxes are recent. Do you think it might be a DIY project? The driver cut outs for the mid and tweeter are really off base too on the 3F.

....and some of the drivers are from the late 70's. The glue around one of the terminal boards is not original either. Perhaps old DIY projects. 

Roy

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I like to think that my historical/chronological knowledge of AR from 1954-1980 (through the Verticals) is about as thorough and accurate as it gets.

I like to think that, but it's not always true.

The AR-3F, from what I've heard, was an early attempt by AR to make a 3a with a "flat" (hence 'F') response. I think it was just before the ADDs (10π, 11) and if it was an attempt based on the old non-ferro-fluid hard paper 3/4" dome, it would have been impossible. That tweeter could not handle the power, nor did it have the efficiency, to have sufficient output to be part of a 'flat' 3a-based system. The early 10 and 11 tweeters (which may not have been fluid-cooled) were nonetheless far more efficient and had greater power-handling than the 3a/LST tweeter, so the ADDs had essentially 'flat' response. Certainly once those tweeters were ferro-fluid-cooled, they simply cruised.

This 3F may be a prototype of that speaker, never in production. Who knows where it came from. When AR left MA for CA in 1993, all the remaining Canton MA production references and lab prototypes ended up at a Waltham MA electronics surplus clearance house, for sale to the public. I could have bought Bx/Bxi/Spirit/Classic (the 1992 Classics, not what we call the 1954-74 Classics) etc. references and protos if I'd wanted. Perhaps this 3F is something like that--a one-off that somehow made it out into private hands. That's my guess.

Steve F.

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11 hours ago, Steve F said:

I like to think that my historical/chronological knowledge of AR from 1954-1980 (through the Verticals) is about as thorough and accurate as it gets.

I like to think that, but it's not always true.

The AR-3F, from what I've heard, was an early attempt by AR to make a 3a with a "flat" (hence 'F') response. I think it was just before the ADDs (10π, 11) and if it was an attempt based on the old non-ferro-fluid hard paper 3/4" dome, it would have been impossible. That tweeter could not handle the power, nor did it have the efficiency, to have sufficient output to be part of a 'flat' 3a-based system. The early 10 and 11 tweeters (which may not have been fluid-cooled) were nonetheless far more efficient and had greater power-handling than the 3a/LST tweeter, so the ADDs had essentially 'flat' response. Certainly once those tweeters were ferro-fluid-cooled, they simply cruised.

This 3F may be a prototype of that speaker, never in production. Who knows where it came from. When AR left MA for CA in 1993, all the remaining Canton MA production references and lab prototypes ended up at a Waltham MA electronics surplus clearance house, for sale to the public. I could have bought Bx/Bxi/Spirit/Classic (the 1992 Classics, not what we call the 1954-74 Classics) etc. references and protos if I'd wanted. Perhaps this 3F is something like that--a one-off that somehow made it out into private hands. That's my guess.

Steve F.

This sounds feasible. I would guess when prototyping several at least were made with variations in crossovers. 

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