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AR tweeter swapping, will this work?

lumpy said:
It is a 8 ohm tweeter, with the identical back wiring. It is a late Teledyne era AR-2ax tweeter.
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Yep ... Sounds like a perfect match!!

One other little thing that has been bothering me about those LST's. Frank on the CSP's has been blowing tweeters like crazy in his LST's. Willy, some day you should put a scope on your amp while it's driving your LST's hard.

What you would be looking for is a high frequency parasitic oscillation caused by an incompatibility between your amp and the LST's transformer and huge cap bank.

Regards,
Jerry
 
Interesting onplane, I will do that. Where would I put the probes? Do you, by chance know of a screenshot where I can see a parasitic oscillation waveform? If not, I would post my waveform here.

Nice to have knowledgeable people on this board, keeps the expensive and $illy mistakes to a minimum. Thanks guys!
 
HepcatWilly said:
Interesting onplane, I will do that. Where would I put the probes? Do you, by chance know of a screenshot where I can see a parasitic oscillation waveform? If not, I would post my waveform here.

Nice to have knowledgeable people on this board, keeps the expensive and $illy mistakes to a minimum. Thanks guys!
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Well, you always have to be careful with scopes, as many use 3 prong plugs and nail the ground lead to earth. Old reel-to-reel tape decks don't like this very much. So either, float the ground on your scope or disconnect everything from your amp except the one source you will use (and don't use a reel-to-reel).

Then put the scope ground lead on the BLACK speaker output and the scope probe on the RED speaker output. Do this first on a non-LST speaker and get accustomed to looking at the audio signal.

Then connect the LST's and do the same. What you are looking for is a big high frequency swing. So make sure you raise the sweep frequency, because any oscillation that's killing tweeters would be pretty high.

I'll be honest, I'm a big AR fan, but I really don't care much for that transformer and cap bank. Early on AR's LST's were killing amps and they kept messing with the cap bank to make the load better behaved.


Regards,
Jerry
 
onplane said:
One other little thing that has been bothering me about those LST's. Frank on the CSP's has been blowing tweeters like crazy in his LST's. Willy, some day you should put a scope on your amp while it's driving your LST's hard.
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Willy's got a pair of the LST2. I'm not real familiar with the LST or LST2, but the LST2 was a nominal 8 ohm load, like the AR-5. I'd hope it wouldn't be as hard to drive.
 
winters860 said:
Willy's got a pair of the LST2. I'm not real familiar with the LST or LST2, but the LST2 was a nominal 8 ohm load, like the AR-5. I'd hope it wouldn't be as hard to drive.
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Hi, Winters!

Actually the "nominal impedance" for the LST/2 is 8-16 ohms depending upon switch position.

Problem isn't the drivers, Winters. It's that transformer and cap bank.

If I had either LST, first thing I'd do is yank the transformer and cap bank. Power the woofer and it's low pass filter with one amp. Add padding to the mid driver circuit. Then drive both mids and tweeter with a separate amp.

With this scheme, you get:

1. a very reasonable load for both amps
2. no chance of any ocsillations caused by the tank circuit of transformer and cap
3. far, far more voicing control than you get with a 3 or 6 position switch​

Regards,
Jerry
 
onplane said:
Actually the "nominal impedance" for the LST/2 is 8-16 ohms depending upon switch position.
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Thanks for the clarification, Jerry. Someday, I'd like to hear the LST or LST2 "in the flesh" as it were.

onplane said:
Problem isn't the drivers, Winters. It's that transformer and cap bank.

If I had either LST, first thing I'd do is yank the transformer and cap bank. Power the woofer and it's low pass filter with one amp. Add padding to the mid driver circuit. Then drive both mids and tweeter with a separate amp.
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Color me surprised. :D
 
winters860 said:
Color me surprised. :D
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You are right, Winters!!

I admit it. I'm a big fan of passive bi-amping. I like it, because of the control over voicing one gets on these classic AR's.

Those LST's, however, are a totally different animal.

Bi-amping there solves all kinds of problems that the transformers/cap bank create. Take the LST/2. The drivers come from the AR-5 and they are very good. Like you, I'd love to hear a set of those.

Regards,
Jerry
 
I would love to hear a set too!

I hooked them up early on, with the blown tweeter, and I'll tell you that they bend sound around corners. Very interested in hearing them complete, then I'll take them down and restore them.
 
Hi guys!
Well, I got lumpy's tweeter the other day, but I had a long lost friend over for the weekend. I popped that baby in tonight and it's a perfect match. The LST/2s sound great!

Thank you all for your help and support, and thanks Dave (lumpy) for sending a pristine, very carefully packed replacement tweeter at a very fair price.
 
winters860 said:
Color me surprised. :D
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Sorry Jerry but that's funny :lmao: You are persistent. I'm not as familiar with LST's but understand they are the pinnacle in many opinion of the AR speaker. That may not be success worth messing with :scratch2:
 
How many ohms are the three quarter inch dome tweeters? What is the acceptable range? I am trying to match a tweeter that now measures 4.2.
Serial numbers are 1689XX.
Roy?
 
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