Shacky Posted June 3, 2006 Report Share Posted June 3, 2006 I just picked up a pair of AR 2ax's from a local speaker shop. I only paid $10 for the pair - they were sitting on floor in the corner and I was told they weren't for sale - they had "issues". Whe I got them home I was thrilled to see that they were consecutive SN's. Then I openned them up and see that one has the older taped magnet woofer with adaptor ring and one has the newer square magnet. The one with the older magnet has plywood fornting on cabinet and one with newer magent has what looks like MDF.Then the real puzzler is the one with the older woofer is the later SN! I would have thought that womone just grabbed an older woofer at wome point fro replacement but the cabinet fronting material and routing don't make sense. If the SN's were reversed I could almost surmize that this was exactly when AR made the switch in components. The the SN not matching up to that story it seems puzzling - or maybe someone just swapped SN's at some point.Any thoughts? Link to comment Share on other sites More sharing options...
Andy Posted June 3, 2006 Report Share Posted June 3, 2006 SN's of 153,000 are about 1971. They must have been made at a change over time with one speaker having the newer inspection sheet and cabinet construction. AR would have had many parts in inventory for production. I've seen other AR's and KLH's with close numbers, but differences in the speakers. Also; check for a date on the back of the tweeters to help pin down the age ? Link to comment Share on other sites More sharing options...
Shacky Posted June 3, 2006 Author Report Share Posted June 3, 2006 I took one of the tweeters out - it does not seem to be working. The date is not very legible. It's definitely 7x but can't make out the x. The midranges do not have the resistors I've seem on some historical reviews. I thought all the later 2ax's had the resistors on the midrange because of the more efficient woofers. Link to comment Share on other sites More sharing options...
charger3834 Posted June 4, 2006 Report Share Posted June 4, 2006 >I took one of the tweeters out - it does not seem to be>working. The date is not very legible. It's definitely 7x >but can't make out the x. The midranges do not have the>resistors I've seem on some historical reviews. I thought all>the later 2ax's had the resistors on the midrange because of>the more efficient woofers.>>OK here's the deal, 153xxx one does date back to 1971. Try to read the serial number on the newer one again, it should exceed 200xxx. It was produced much later and in the Norwood factory as opposed to Cambridge. I believe it should read 253xxx. This speaker dates to 1974. You can confirm this by the "EIA" number on the same label which tells you the week and the year it was manufactured. The 1971 ALNICO "Slug" woofer with the adapter ring will match up to a midrange that measures about 6.5 ohms DCR. The speaker with the ceramic-ferrite woofer will match up to a 3.5" midrange that is otherwise identical, but measures about 8.9 ohms DCR.As the ceramic-ferrite woofer repaced the earlier ALNICO Slug woofer, AR initially added two sand cast resistors to the mids leaving everthing else in the system the same. They then changed the impeadance of the mid itself. It looks like this change occured between 250xxx and 254xxx. I took me a while to figure this out too.One must conclude that you have one of each sub-variant of the "new" post-1970 AR-2ax. Link to comment Share on other sites More sharing options...
Shacky Posted June 6, 2006 Author Report Share Posted June 6, 2006 It may very well be that the later style cabinet is a service replacement. I've attached a re-balanced image of the serial number and label - also has the EIA number which might be 78 at the end - 1978? The serial number is a hand written number so this may be the reason for the differences. I would think that the mirdanges would be a real mismatch for the customer. The newer cabinet's midrange is much louder - does that make since for a higher impedence driver?Jim1338.txt Link to comment Share on other sites More sharing options...
charger3834 Posted June 6, 2006 Report Share Posted June 6, 2006 Interesting ! That serial number does not fit with the vintage of that system. I am just starting to get a handle on this EIA stuff, as this practice started later on, so I don't want you to take this as gospel, but I think the middle number should be the year.As for the midrange, the Ceramic-ferrite magnet woofer does seem to have stronger midrange output than the Alnico slug version. I think this is why AR increased the resistance on the 3.5" CTS midrange. I had a pair of 1974's that had the ceramic-ferrite magnet woofers. One had resitors attached to the 6.5 ohm mid, and the other had the 8.9 ohm mid. Since the stuffing, caps and number 7 coil were all the same as earlier post 1970 versions. I installed 1972 alnico slug woofers and 6.5 ohm mids in that pair. I liked the way it turned out. I can always go back the other way as I located another 8.9 ohm mid(mid with resistors failed) and I can always refoam the original ceramic-ferrite magnet woofers. So in conclusion, you do see some evolution in the post 1970 AR-2ax. Link to comment Share on other sites More sharing options...
charger3834 Posted June 6, 2006 Report Share Posted June 6, 2006 I don't think the variation would be a big problem for the customer, the difference was subtle and AR was pretty careful about those things. I wish we did have an official explanation; I only stumbled upon this phenomenon by accident. I then compared notes with Tom Tyson and Roy C and made sure I had my facts straight. I also make notes on ebay pictures. I don't like ideas that can't be substantiated, I really want to try and preserve historical correctness. Link to comment Share on other sites More sharing options...
Shacky Posted June 6, 2006 Author Report Share Posted June 6, 2006 Well thanks for all your time on this. I picked these up for $10 so I really didn't have high expectations. Then when I saw the consecutive SN's I started getting a little more excited.Now I need to figure out what to do with these. I brought the woofers to Carl for refoaming. I need at least one new tweeter and may need a midrange and woofer too. It would have almost been easier to pick up complete set of drivers - I've seen more of the old style lately - but then I worried about the different crossovers on post 70 model.Guess I'llwait to see how the r-foam goes then figure out the rest.Do you recomend replacing the caps? Link to comment Share on other sites More sharing options...
charger3834 Posted June 7, 2006 Report Share Posted June 7, 2006 Don't put the old 10" cast-aluminum cloth surround woofers in. They are a different animal, as I have outlined the other recent AR-2ax post. Besides, they will only fit it the older cabinet with the oversized hole. Why don't you try and find two of the comman 4 bolt ALNICO Slug-magnet woofers(1970-1973). Then get two of the comman 6.5 ohm mids (1964-1974). That will give you a balanced pair.As for the caps, that is a debate for greater minds than me. I guess sometimes they change in value a bit over time. Lots of times they stay well within spec. Why don't you test them, if they held their spec for 35 years, why bother replacing them ? You could probably do nothing at all and be fine. Go for it if you want ! Link to comment Share on other sites More sharing options...
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