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A Beovox MS150 Project

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sonavor
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sonavor posted on Fri, Mar 30 2012 5:31 AM

While delaying the completion of the Beomaster 6000 project (I have been recapping some other amplifiers before diving into the volume motor repair), I came across these Beovox MS150 speakers that are in need of restoration. The MS150 speakers have been on my radar for a while now but this was my first chance to get a pair and they were within driving distance (for me) to pick up...so no shipping. 

As you can see, the 8 inch and 10 inch drivers need new foam surrounds. That is to be expected. I haven't opened them up to check the crossovers yet but I am figuring I will be replacing those capacitors as well.  The real issue I will have is the top grill covers. Both speakers are missing those. Even without them I had to buy these speakers. If anyone has any spare top grill covers please let me know. 

I am also trying to decide the best place to order surrounds. I have bought surrounds off Ebay for several of my CX100, CX50, S55, S120.2 and RL140 speakers.  All of those refoam projects came out great. I imagine the same surrounds for the S120.2 8 inch driver should also work for the MS150. I will see if that company also supplies the 10 inch surrounds. 

In any case, parts will have to be ordered so it will be a couple weeks before I can really get started.  


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sonavor
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...with the grill covers (no top cover)


Peter
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Answered (Verified) Peter replied on Fri, Mar 30 2012 9:06 AM
Verified by Jason

When I had a pair of these, I had them reconed with a rubber surround. The sound was excellent - Recone Lab were so impressed they put them through their sound chamber - ruler flat response! They are the pair pictured here.

Peter

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sonavor
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I attached the first 8 inch foam surround to the cone today.  The fit was very tight.  I marked where then inner foam ring edge covers the cone and it appeared to be the same distance all around.


sonavor
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On this first surround I applied the glue to the underside of the foam surround. It is angled to meet the angle of the cone.  In the picture with the glue I had to snap a quick picture just to show what the glue looked like.  Before I attached the surround I made sure it was spread evenly.  The glue I have used on all my refoam projects is some glue I got from Simply Speakers.  I know some people on the forum here haven't liked their surrounds but I have bought glue and grill cloth fabric from them and had good success.  Their glue is clear and sets up very quickly.  It stays down when you press it in place too. 

The second picture shows the surround glued to the cone.


sonavor
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Next I glued the 10 inch surround to the 10 inch woofer cone. The 8 inch driver cone is a plastic type material (very smooth).  The 10 inch driver cone is more of a paper type material.  The surround for the 10 inch woofer looked like a good fit but the amount of foam surround that contacts the cone is less that what the 8 inch driver had.  On the 10 inch surround I applied the glue to the edge of the cone making the width of the glue trail the width of the old glue markings.  The surround attached nicely.  I went over the glued area several times as it dried to make sure there were no air pockets and everything was nice and smooth.


sonavor
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Now....bad news

As I prepared to attach the surround on the second MS150 8 inch driver I noticed the cone was frozen.  It doesn't budge.  I opened the dust cap and sure enough one side looks fused together.  It must have happened when I was handling the driver during cleaning I think because I'm sure it was okay when I pulled it out of the cabinet.  Quite disappointed.

I will have to temporarily borrow one of the 8 inch drivers from my S120.2 speakers later when I am ready to test these MS150's.  I will finish the other 10 inch driver surround then prepare the shims.


sonavor
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Continuing on with the other three woofer drivers that are ready to shim, I started with the 10 inch driver that is from the cabinet with the ruined 8 inch driver. 

I picked up some sheets of acetate from my local art supply store.  They only carried three sizes: 0.003 gauge, 0.004 gauge and 0.005 gauge.  So I bought one sheet of each.  Starting with the 005 gauge I cut a strip that was 5 cm wide and 11 cm long.  I cut away the dust cap of the driver and inserted the acetate strip in the slot the cone travels. It fit easily.  Next I cut three shorter 5 cm wide strips from the 003 gauge acetate to position evenly around the gap. That made the fit so it was snug but I can still move the cone.  So I think I'll replace the 003 gauge strips with 004 gauge strips.  My understanding is that the shims will ensure an equal distance of the cone around the pole (is the right terminology?).  With the shims in place I should be able to position the cone so the top is level and the outer edge of the surround is exactly where it needs to be glued to maintain that position.

Here is a picture of the acetate shims on the 10 inch driver.


sonavor
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I tried out the 004 gauge shims instead of the 003 shims but there wasn't enough space.  So the shims I am using are the 005 + 003 gauge acetate strips.  Since those fit nicely (all the way to the bottom) where the cone is straight and level I went ahead and glued the surround to the frame.  Tomorrow I will give the driver a test. 


Søren Mexico
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Nice clean job John

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sonavor
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Thanks Søren. 

Today I removed the shims.  What a great feeling to try out the movement and see that the travel feels perfect.  I hooked the driver to a signal generator and pumped it with a 0.4v sine wave from 20 Hz to around 160 Hz.  It sounded just as I expected it to.  I must say using the shims worked as well as advertised and I feel more secure in the repair having seen the cone evenly spaced around the pole.

I still have the other 10 inch driver and the remaining good 8 inch driver to finish the surrounds on.  It is really tempting to not do shims on those two because their movement with the surrounds only attached to the cone move without any rubbing.  No worry though, I will go ahead and use shims on them.  I am curious on the 8 inch driver anyway because I want to see what a good one looks like under the dust cap.

Here is a picture of the completed first 10 inch driver.  The cone is a little ragged from age.  There are a couple of spots on the dust cap that are brownish.  I think they were spider eggs.  I tried cleaning them off but I might have to eventually put on a new dust cap.  The glue I used around the dust cap where I made the cut is Aleene's clear tacky glue but the old glue underneath it yellowed.  It is still drying so I'll see what it looks like tomorrow.


sonavor
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Update on the bad 8 inch driver....

Tonight I took apart the 8 inch driver with the frozen cone.  First I cut away the spider from the frame and un-soldered to two leads from the cone to the frame connection points.  The cone and voice coil assembly still wouldn't budge.  So I pulled the spider and cone from the voice coil.  I checked the gap between the center pole (doughnut in this driver's case) and the voice coil with my acetate sheets.  They wouldn't go all the way around as I was sure they wouldn't. There was no way to get the voice coil out because the center, doughnut shaped pole was leaning against it.  With nothing really to lose I tried my channel lock pliers by bracing one side to the side of the driver frame and the other inside the doughnut. As I slowly squeezed the pliers shut the center pole rocked away from pinching the voice coil.  The pole stayed where I had rocked it and the voice coil easily removed. 

Here is a picture of everything apart.


sonavor
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Here is a picture of the straightened center pole and the voice coil removed.  The upper ring area of the voice coil (above where the wire windings are) is pulled away. 

The question now is can this driver be repaired.  I would think the voice coil could be repaired and re-attached to the spider and cone.  I'm not sure about the center pole that I was able to rock back into place.  Why was it loose?  Since I can only move it with pliers would it function okay as a woofer if the other pieces were repaired?  Or would it eventually rock back against the voice coil and freeze up the cone again?  I know of a good speaker repair shop about an hour and a half drive from me.  I spoke to them on the phone yesterday and they really haven't done any work on a Peerless driver before (this 8 inch driver was made by Peerless for B&O).  However, they are very experienced speaker shop (45 years in business) so it might be worth taking over to them.


sonavor
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Here is a picture of the voice coil assembly separation from the other side (the inside of the tube).  It looks repairable to me. The gap/channel where the voice coil moves is a lot wider on this 8 inch driver than on the 10 inch driver I just finished the surround on. I think there would be enough room add material to repair the voice coil assembly and still slide in and out of the channel.  The question is still about the integrity of the center pole and if it needs anything done to it. 


sonavor
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This morning the glue on the dust cap of the re-foamed 10 inch driver is dry and the yellowish coloration where I glued is gone.


h1npw
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h1npw replied on Fri, Apr 13 2012 5:51 PM

"When I had a pair of these, I had them reconed with a rubber surround. The sound was excellent - Recone Lab were so impressed they put them through their sound chamber - ruler flat response! They are the pair pictured here."

I am now the extremely happy owner of these - they put a smile on my face most days.

I wish you every success with the restoration and your relationship with your neighbours!!

Cheers

Nigel 

h1npw
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h1npw replied on Fri, Apr 13 2012 6:11 PM

BTW - Great thread & photos!

Cheers

Nigel

 

Søren Mexico
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About the voice coil, I would try to repair it with thin paper (bible paper) on both sides with epoxy, then find a plastic tube that fits inside, to get it nice and circular again, eventually you will have to sand down the epoxy to get it thin enough.

The center pole, is it possible to epoxy it all around at the arrow, I cant see what material you have at bottom, but if you epoxy it make sure it is centered.

Then get a new spider, cut the outer D to fit, then, with a circle, mark and cut the center hole, shim the voice coil (hard fit) and position it exactly in the heights and glue it to the spider, let dry and then glue the spider  to the basket. When dry glue the cone carefully centered to the coil, when dry, glue surround to cone, when dry, reshim to light fit and glue surround to the basket.

I would not leave the center pole as it is now, it may come loose again.

 


Collecting Vintage B&O is not a hobby, its a lifestyle.

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