Restoring a set of AR LST

[genek]

Not me... like many audiophiles, I lusted and saved for speakers. Fixed and traded to get my LST's, which were being sold by a dealer for $600/pr.

And then started blowing them up.

I wish I could have back every toy I ever destroyed in my youth, magically restored to good working condition. I could probably make a good retirement income selling them off on eBay now.

[Cube4Square]

Or got tired of replacing blown tweeters.

That would make sense if he had only sold the speakers, but he also sold his recently purchased Amp/Preamp that were in good working order, so I think it had to be more than some frustration with just the speakers themselves. He went to the trouble of having the entire crossover and almost all the tweeters replaced, so that sounds like someone dedicated to AR at the time. As well, since then, the 2nd owner only had the woofers repaired, so the last updates and the new amp/preamp were solid changes that the original owner would most likely have stayed with unless some major financial event caused him to sell.

[Pete B]

That would make sense if he had only sold the speakers, but he also sold his recently purchased Amp/Preamp that were in good working order, so I think it had to be more than some frustration with just the speakers themselves. He went to the trouble of having the entire crossover and almost all the tweeters replaced, so that sounds like someone dedicated to AR at the time. As well, since then, the 2nd owner only had the woofers repaired, so the last updates and the new amp/preamp were solid changes that the original owner would most likely have stayed with unless some major financial event caused him to sell.

You might find the letter from Roy Allison interesting in this post:

http://www.classicspeakerpages.net/IP.Boar...&hl=allison

I have to wonder if the auto-transformer saturated with big muscle amps like the Phase Linear 700.

They could also cause the protection circuitry to trip when over driven.

[genek]

That would make sense if he had only sold the speakers, but he also sold his recently purchased Amp/Preamp that were in good working order, so I think it had to be more than some frustration with just the speakers themselves. He went to the trouble of having the entire crossover and almost all the tweeters replaced, so that sounds like someone dedicated to AR at the time. As well, since then, the 2nd owner only had the woofers repaired, so the last updates and the new amp/preamp were solid changes that the original owner would most likely have stayed with unless some major financial event caused him to sell.

Maybe Dad was also "dedicated to AR," and cut off Sonny's allowance after he took Dad's $600 LSTs to school, blew up all their tweeters, modded the crossovers and spent money that was supposed to go toward school expenses on a new amp and preamp.

[Zilch]

Hard to say for sure the exact scenario, but I imagine the original owner may have had a lesser quality amp during his college days perhaps. He literally lived in a house that bordered the University, so I can only imagine there were some "rockin" days. In April of '78, he bought the Phase Linear Amp/Preamp in Athens, GA, then apparently graduated/moved to Richmond, VA which is where the 2nd owner bought them, so also odd to me that the original owner sold his fairly new system after a year or less (person I bought them from recalls getting them in '78/'79 timeframe), so he either had a lot of disposable income or life after college was more difficult than anticipated. ;-)

Despite their 1200W rating, a late-70s college-age rocker could easily blow up LSTs with a Phase Linear amp. At that point, what's the answer? "Upgrade" with new crossovers and tweeters having better power handling. Maybe we then smoke more of the original tweeters, or some of the new ones, as well. In any case the, the thrill is gone, and it's time to move them out in favor of something more appropriately suited to the owner's listening preferences.

In any case, it would appear that AR-11 used a switched-resistor attenuation network not unlike that posted by the Zilchster for earlier models in lieu of the troublesome pot:

http://www.classicspeakerpages.net/IP.Boar...?showtopic=4681

And most interestingly, Allison himself provided the requisite values for having AR3a play flat in 2000....

[genek]

In any case, it would appear that AR-11 used a switched-resistor attenuation network not unlike that posted by the Zilchster for earlier models in lieu of the troublesome pot:

And most interestingly, Allison himself provided the requisite values for having AR3a play flat in 2000....

The LST in 1972 was the first AR speaker I saw that used switched level settings (with the autotransformer) instead of pots. By the time the ADD series came out, they all had them, but with resistors. I think the only AR speaker made after that with cintuously-variable level controls was an L-pad equipped "3a Limited" that according to Minh was manufactured under license by AR's Asia distributor for sale there and never available in the US.

Allison's fixed resistor values appear to be the equivalent of the pot resistances for the white dot "normal" settings, which we know is not flat. I think he just misread the question.

[soundminded]

I raised that possibility earlier, but I think the mismatched tweeter set that includes an original 3a/LST driver argues against that. If this had been done at the factory during the ADD years or later, one tweeter that old would not have been used. My vote for the most likely scenario is someone with an original 3a-based unit repeatedly blowing out tweeters, replacing them over a period of time with later drivers as the originals became unavailable and eventually replacing the crossovers.

"My vote for the most likely scenario is someone with an original 3a-based unit repeatedly blowing out tweeters, replacing them over a period of time with later drivers as the originals became unavailable and eventually replacing the crossovers."

Now who would do such a thing? Got any likely candidates you know of?

Why not "round up the usual suspects" Maybe one of them will come forward and....fess up!

[Zilch]

By the time the ADD series came out, they all had them, but with resistors.

By my experience, the approach has been singularly under-appreciated....

[soundminded]

By my experience, the approach has been singularly under-appreciated....

Replace them all with waveguide tweeters. Zilchify it!

[genek]

By my experience, the approach has been singularly under-appreciated....

If these were mine, I think what I would want to do is determine the resistors necessary to produce the same mid and high attenuations as the original autotransformer crossover, then wire them "Zilch-like" to rotary switches in the original front openings, if for no other reason than the probable difficulty in finding replacements for the autotransformers. Then I'd figure out which type of tweeter the pair had the most of and start prowling the auction site for enough to make a matched set. I could live with different AR domes and controls that looked original and produced similar sonic effects, but no way would I be satisfied with mismatched tweeters and three-way switches on the backs.

[Zilch]

Replace them all with waveguide tweeters. Zilchify it!

Getting warm, SM.

[They'd smoke Howard's Allisons, too, little doubt.... ]

[soundminded]

Getting warm, SM.

[They'd smoke Howard's Allisons, too, little doubt.... ]

"They'd smoke Howard's Allisons, too, little doubt.... "

And what are you smoking?

http://www.parts-express.com/pe/showdetl.c...tnumber=279-060

[Zilch]

And what are you smoking?

http://www.parts-express.com/pe/showdetl.c...tnumber=279-060

Wrong stuff, SM.

For those unskilled in the art such as yourself, this might actually get somewhere:

http://www.madisound.com/catalog/product_i...roducts_id=8322

Carl has already demonstrated how waveguides mitigate the diffraction issues plaguing vintage AR designs here....

[soundminded]

Wrong stuff, SM.

For those unskilled in the art such as yourself, this might actually get somewhere:

http://www.madisound.com/catalog/product_i...roducts_id=8322

Carl has already demonstrated how waveguides mitigate the diffraction issues plaguing vintage AR designs here....

Are you nuts? I never pay more than 50 cents for a tweeter. Just bought 400 3/8" domes at 5 cents each a few months ago. Haven't even tried any of them yet. I still have plenty left over from my 150 or so order at 20 cents each back about a year and a half ago. Those work great. About as good as the Daytons and Audax tweeter's I'd bought at around $5 each. I like the mylar/poly domes in multidirectional arrays. I don't believe in tunneling sound. Not for main speakers anyway. Why not just run a pipe from your speakers to your ears instead? Cut out the room completely

[Zilch]

Are you nuts?

No, "competent" might be apt, by contrast, however.

It's you who was just railing against AR's fake FRs; there's DXT in an actual system, above.

Just a guess, but they'd likely fix LST/AR3a quite nicely, but on your 50¢ budget, we'll never know....

[kkantor]

I wish I could have back every toy I ever destroyed in my youth, magically restored to good working condition.

I feel that way about most of my brain and body. Several relationships, too.

But, I've owned a fair amount of audio gear I really never want to see again. Fortunately, almost no AR stuff is in that category!

-k

[genek]

But, I've owned a fair amount of audio gear I really never want to see again. Fortunately, almost no AR stuff is in that category!

I'm not saying that I'd want to keep all the stuff I've let go or lost over the years, but just about all of it has a become collectible to someone and would have a resale value way beyond what simple inflation could account for.

[Zilch]

HUH?

It's about the MONEY?

[Who'd have thought...? ]

[genek]

HUH?

It's about the MONEY?

[Who'd have thought...? ]

I wish I had at the time...

[Mexicomike]

I wish I had at the time...

I sold a 1966 Plymouth Hemi Belvedere for 1800 bucks in 1970...

Looked exactly like this one: http://www.cars-on-line.com/28707.html

Oh well, who knew?

[mluong303]

Can you take high resolution pictures of the entire back of both speakers. There are so few screw holes being drilled on the back to attached the original AR-LST Xover. That was why I suspect these were prototype with the newer crossover boards when I first see your posted pictures. Do the 2 center grill panels have small hole punched through which indicate the used of the original 6 position switch? Post pictures of the 2 center grill panels as well if you could.

Minh Luong

I just locate this picture in my old CD showing the very last version of AR-LST speakers being made when AR ran out of epoxy boards and replace with masonite crossover board with the autotransformer set on the same board with only 5 screws attached from the back which maybe same as the two cabinets you have.

Minh Luong

[Cube4Square]

I just locate this picture in my old CD showing the very last version of AR-LST speakers being made when AR ran out of epoxy boards and replace with masonite crossover board with the autotransformer set on the same board with only 5 screws attached from the back which maybe same as the two cabinets you have.

Minh Luong

Here are pics of one, front/back, but they are both the same. It looks as though the patched screw holes on the back match your pic.

[Cube4Square]

About what year were the last series of LST's manufactured?

[genek]

About what year were the last series of LST's manufactured?

1976

[Cube4Square]

1976!? Wow, these things surely went through hell right out of the gate, then were sold only two years later.

Well, at this point, I think I'll take the path of least resistance and look for that "matching" 8th tweeter, put new caps on the current crossover, refoam the woofers and do any cosmetic repair to make them presentable. Given these are not originals, I'm not as concerned now about messing them up, but, I do have a head start on some other speakers, so these will probably be second in line for project work.