mike tarelli Posted April 30, 2012 Report Share Posted April 30, 2012 Finally managed to find a pair of LSTs. A 700 mile round drive bought me front wired original units,good cabinets,labels in place,boxes and literature.Serial numbers HL 2779 and HL 2780.Original owner.I re-foamed the woofers,polished the front plates and I thought all I had to do was order some linen from 123 stitch.However there is a nasty "rasping" sound from the tweeter in one cabinet and the same from a mid in the other. Not there all the time but very apparent on something like piano or flute.I noticed the tweeter first and had a look on Vintage AR. There are the HI-Vi units listed but also something different (and new to me) for the LST.Does anyone know anything about them? Surely the tweeters are the same as the AR3a. It also suggests only fitting one unit.The serial numbers are HL 2779 and HL 2780.Oh yes both fuses were blown.I would appreciate some suggestions and advice on how to proceed. I am in the U.K.Thanks,Mike. Link to comment Share on other sites More sharing options...
Tetrode Posted April 30, 2012 Report Share Posted April 30, 2012 If I was in your position I would recap them first.That may fix the problem. Link to comment Share on other sites More sharing options...
RoyC Posted May 1, 2012 Report Share Posted May 1, 2012 Finally managed to find a pair of LSTs. A 700 mile round drive bought me front wired original units,good cabinets,labels in place,boxes and literature.Serial numbers HL 2779 and HL 2780.Original owner.I re-foamed the woofers,polished the front plates and I thought all I had to do was order some linen from 123 stitch.However there is a nasty "rasping" sound from the tweeter in one cabinet and the same from a mid in the other. Not there all the time but very apparent on something like piano or flute.I noticed the tweeter first and had a look on Vintage AR. There are the HI-Vi units listed but also something different (and new to me) for the LST.Does anyone know anything about them? Surely the tweeters are the same as the AR3a. It also suggests only fitting one unit.The serial numbers are HL 2779 and HL 2780.Oh yes both fuses were blown.I would appreciate some suggestions and advice on how to proceed. I am in the U.K.Thanks,Mike.Mike,Try swapping the funky sounding tweeter with a good one from the other cabinet to see if the problem follows the tweeter or remains with the cabinet.Vintage AR's new listing is the standard AB Tech 3/4" replacement tweeter with some modifications.http://www.abtechservices.com/arspeakers.htmlRoy Link to comment Share on other sites More sharing options...
mike tarelli Posted May 1, 2012 Author Report Share Posted May 1, 2012 Hi Tetrode,I was afraid someone would say that. Busy checking over a hundred back pages! Never done a re-cap.Thanks,Mike. If I was in your position I would recap them first.That may fix the problem. Link to comment Share on other sites More sharing options...
mike tarelli Posted May 1, 2012 Author Report Share Posted May 1, 2012 Mike,Hello Roy,Stupid of me not to think of it. Of course, I'll try. I'm guessing the AB tech tweeter is used because it's the right impedance.Picking up a lot from back threads.Many thanks for the information.Mike.Try swapping the funky sounding tweeter with a good one from the other cabinet to see if the problem follows the tweeter or remains with the cabinet.Vintage AR's new listing is the standard AB Tech 3/4" replacement tweeter with some modifications.http://www.abtechser...arspeakers.htmlRoy Link to comment Share on other sites More sharing options...
RoyC Posted May 1, 2012 Report Share Posted May 1, 2012 Mike,The AB Tech tweeter is being used because other tweeters, like the HiVi's, do not work. The parallel coil approach used with them negatively affects the LST crossover. The ABT tweeter with added dampling material under the dome, as well as an added series capacitor and resistor, comes closest to the original.Vintage AR/Larry Lagace and I have been communicating on this issue for the past couple of months. There is still a problem, however, when replacing more than one tweeter per cabinet.Roy Link to comment Share on other sites More sharing options...
mike tarelli Posted May 2, 2012 Author Report Share Posted May 2, 2012 Mike,The AB Tech tweeter is being used because other tweeters, like the HiVi's, do not work. The parallel coil approach used with them negatively affects the LST crossover. The ABT tweeter with added dampling material under the dome, as well as an added series capacitor and resistor, comes closest to the original.Vintage AR/Larry Lagace and I have been communicating on this issue for the past couple of months. There is still a problem, however, when replacing more than one tweeter per cabinet.RoyHi Roy,Thanks for the information and your input on this issue. It's bound to be needed by LST owners.However perhaps not yet for me! As you suggested I swopped the funky tweeter and it sounds fine in the other cabinet. Took the woofer back out to introduce myself to the caps:6uf2 x 20uf which makes 40uf I assume150uf2500mfd.It appears uf and mfd are the same thing and I have a late x-over.The booklet that came with the speaker shows 5000mfd instead. Wilmslow Audio over here should be able to supply new caps.Now if I can just keep my nerve!Many thanks to you and Tetrode,Mike. Link to comment Share on other sites More sharing options...
JKent Posted May 2, 2012 Report Share Posted May 2, 2012 Hi MikeBefore you go tearing into things wait for some more input from Roy and others who have worked on the LST (I have never had the pleasure myself). You've already determined you have the later xo. I looked at the schematic and found this list of caps:C1 6uFC2 40uFC3 150uFC4 1uF 100vC5 200 uF 100vC6 & C7 combination 2x5000uFYes--uF and mfd both mean microfarad (that "u" should be the Greek letter "mu").You don't need to be concerned about voltage ratings--higher is better (usually)The small values should be replaced with film caps. For the 150uF many people use non-polar (aka bipolar) electrolytics (aka NPE). They are smaller and cheaper than film.The 5000uF will be a challenge. I believe there has been discussion here. Suggest you search and again, see what those with experience say. Wilmslow seems to stock NPEs up to 80uF. On this side of the pond Madisound has 1,000uF NPEs.Take a look at this post from Minh:http://www.classicsp...?showtopic=4198Klaus has some photos here, and explains the two 5000uF caps (they are in series to halve the capacitance and double the voltage):http://www.classicsp...?showtopic=2201If your 2500uF caps are those big ol' screw terminal Sprague compulytics they may very well still be good. Think I would replace the lower values with good film caps but leave those.Good luck with the restoration!Kent Link to comment Share on other sites More sharing options...
mike tarelli Posted May 2, 2012 Author Report Share Posted May 2, 2012 Hi MikeBefore you go tearing into things wait for some more input from Roy and others who have worked on the LST (I have never had the pleasure myself). You've already determined you have the later xo. I looked at the schematic and found this list of caps:C1 6uFC2 40uFC3 150uFC4 1uF 100vC5 200 uF 100vC6 & C7 combination 2x5000uFYes--uF and mfd both mean microfarad (that "u" should be the Greek letter "mu").You don't need to be concerned about voltage ratings--higher is better (usually)The small values should be replaced with film caps. For the 150uF many people use non-polar (aka bipolar) electrolytics (aka NPE). They are smaller and cheaper than film.The 5000uF will be a challenge. I believe there has been discussion here. Suggest you search and again, see what those with experience say. Wilmslow seems to stock NPEs up to 80uF. On this side of the pond Madisound has 1,000uF NPEs.Take a look at this post from Minh:http://www.classicsp...?showtopic=4198Klaus has some photos here, and explains the two 5000uF caps (they are in series to halve the capacitance and double the voltage):http://www.classicsp...?showtopic=2201If your 2500uF caps are those big ol' screw terminal Sprague compulytics they may very well still be good. Think I would replace the lower values with good film caps but leave those.Good luck with the restoration!KentHi Kent,Many thanks for the information.I'm obviously confused. I was basing my view of the x-over on the 2500 cap. My x-over only has the 6mfd,40mfd,150mfd and 2500mfd. That must make it an old one after the 5000mfd was replaced. Incidently the 3 smaller caps are all Sprague but not the big one! More homework to do. I promise not to rush!Regards,Mike. Link to comment Share on other sites More sharing options...
xmas111 Posted May 2, 2012 Report Share Posted May 2, 2012 Hi Mike, I just finished recapping my LST's a while ago with the help of the guys here. My xovers had the same caps as yours....6mfd,40mfd,150mfd and 2500mfd I ended up using 2 - 1000uf and 1 - 500uf bennic np caps for the 2500uf cap. Here's what the xover ended up looking like.......the pic is in post 22 http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7056&st=20 John Link to comment Share on other sites More sharing options...
KlausDK Posted May 2, 2012 Report Share Posted May 2, 2012 Hi MikeIf you send me your phone number in a PM, I can give you a call; I have restored my LST's a few years back, it is easier to communicate more complex information in that way.BRgds Klaus Link to comment Share on other sites More sharing options...
mike tarelli Posted May 3, 2012 Author Report Share Posted May 3, 2012 Hi Mike, I just finished recapping my LST's a while ago with the help of the guys here. My xovers had the same caps as yours....6mfd,40mfd,150mfd and 2500mfd I ended up using 2 - 1000uf and 1 - 500uf bennic np caps for the 2500uf cap. Here's what the xover ended up looking like.......the pic is in post 22 http://www.classicsp...opic=7056&st=20 JohnHi John,Must be getting punchy. I followed that entire topic in real time. Obviously always been interested in LSTs,but also to admire your skill. Also loved the link to the turntable.I have an XB1.The crossover looks the same for the caps but mine does not have rear access. All the work will have to be through the woofer hole. Great work on your LSTs and thanks,Mike. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.