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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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Correction on picture of 8 inch driver dampening tube.  I was checking my work and realized the plastic driver sleeve for the 8 inch woofer has an indention (lip) half way up the sleeve.  So the I don't think the sleeve goes all the way into the paper tube as I show in the earlier picture.  The tacky glue is slow drying so it was easy to reposition the sleeve where it needs to be.  Here is an updated picture.


sonavor
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Dillen had me check the resistance of the midrange (a 3 inch phaselink driver) to see if it was open.  It was so I took it apart and one of the coil leads had broken off.  Here is a picture of the coil - one lead is still attached and the other is broken.  I will need to scrape a little insulation off and see if I am steady enough to reconnect it (tomorrow).


tournedos
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I just love the pictures. Good luck with the job!

--mika

Step1
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Step1 replied on Mon, Apr 16 2012 5:34 PM

I agree - Great dedication :) BTW while you have those mids apart check the glue between coil former and dome - They tend to separate with age and that would be a shame to happen after putting the thing back together!

Olly

Rich
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Rich replied on Mon, Apr 16 2012 5:39 PM

sonavor:

Dillen had me check the resistance of the midrange (a 3 inch phaselink driver) to see if it was open.  It was so I took it apart and one of the coil leads had broken off.  Here is a picture of the coil - one lead is still attached and the other is broken.  I will need to scrape a little insulation off and see if I am steady enough to reconnect it (tomorrow).

I've read on other sites where repairers of tweeters with broken voice coils just discard the broken bit and unwind the coil one turn.  How many turns do these coils have?  Are there multiple layers?


sonavor
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There is just one layer and 15-16 turns. 

I used the pointed razor knife to scrape insulation material away from the wire I had to join. Then I applied a little flux paste and tinned the bare wire ends.  After that I bent the loose wire where I could hold the coil in one hand with the two bare wire ends side by side. With the other hand I tinned the smallest solder tip I have and applied a bead of solder. 

The first picture shows that first join. It served the purpose of attaching the wires so I could use a little super glue to mount part of the loose wire to the voice coil ring.  That glue dries quickly and I could then work on making a better solder joint.  The second picture shows as it is right now. The wire is joined together pretty good.  I was hoping for a better looking joint but I'm not sure if I want to keep messing with it (I could make it worse).  The solder joint does not stick out farther than the copper wire coil so it shouldn't be a problem.  I don't have any conformal coating (or can't find it) so I can either order some or use some super glue.

With the wire re-attached I measured the resistance across the driver connectors.  I measure 7.2 ohms.


sonavor
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I found my circuit sealer and put a coating over the solder and repaired wire. It looks like the voice coil just lays into the slot of the magnet part and snaps into the plastic frame. Comparing this one to the good one - both measure 7.2 ohms.  I am getting sound out of the repaired midrange now but it isn't right....much to faint.  When I connect a 500 Hz sine wave to the good phaselink the tone is strong even with the voltage level down around 65mV.  The repaired driver is barely noticeable.  I can turn up the voltage level and get get better volume but it doesn't sound the same to me as the good one. It definately won't do as it currently is.

So I must not have the driver put back together correctly or there is some other part of it that is damaged.  The top part of the coil ring has some clear glue residue.  Should the coil be fixed to the rubbery/plastic dome that fits over it?  Is that what you are referring to Step1 ?


sonavor
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In this picture...

Is this how the phaselink midrange driver should re-assemble?  With the rubber/plastic dome laying into the plastic frame, then the voice coil mounting to the inside of the dome?

Since the side of the ring that meets the dome has residue glue on it I am thinking that is what Step1 meant about the coil and dome coming un-glued.  Hopefully that is also the issue with the sound problem.

I won't go any further until I get confirmation but jumping ahead to the next question - Assuming the coil will need to be glued in the position shown in the picture here, Does the magnet part of the driver just slide in and snap into place in the frame?  Or should it also be glued?  The reason I ask is because the magnet had glue on the area near the terminals.


Step1
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Step1 replied on Tue, Apr 17 2012 9:22 AM

Yes Sonavor the coil should be stuck to the dome - otherwise the mechanical energy of the moving coil will not be transferred, which sounds like your current issue! Just make sure the coil sits in its little ridge - it has to be absolutely round without distortion. The dome should be glued to the outer frame, then this whole assembly clips onto the rear assembly.

Olly

sonavor
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I glued the coil in the dome and the dome to the frame today.  For the coil I used the same clear glue I used for the surrounds.  It can take movement but it bonds very fast and doesn't take much for it to hold tight.  I used a Q-tip cut in half at an angle.  I like the original Q-tip that has a solid paper shaft (not a hollow plastic tube like the newer ones).  The paper shaft part is good for mixing glue, applying glue, etc.  With just a dab of glue on the Q-tip end, I slowly applied it to the ridge of the coil that sits in the dome.  For the dome edge that meets the plastic frame I used some Aleene's Tacky glue - the green bottle type that remains tacky (dries clear).  Where the two leads cross the frame to the terminals there was a layer of sticky, blue tinted glue holding the wires in place.  That remaining sticky glue always grabs the magnet assembly and tries to pull up the thin wire leads each time I have taken this driver apart.  That is too risky to accidentally break the leads I think so I covered that glue area with a coat of clear glue that dries flexible but dry.  If I find that I need a little glue for the magnet assembly I will place some around the frame away from the wires. 

Here is a picture of the coil, dome and frame assembly waiting to dry. 


sonavor
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Once the coil, dome and frame assembly is dry I will snap the magnet base assembly back in place in the frame and hopefully have a nice sounding midrange driver.  Here is a picture of the magnet base assembly (for lack of the official terminology).


sonavor
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Success.  I completed the re-assembly of the midrange driver tonight and it works. The tone appears to same as the other midrange now.  I am glad I use the green bottle Aleene's (Tack It Over-and-Over) Tacky glue on the dome lip that mates with the plastic frame.  To get the voice coil into the magnet base I needed to have the dome and coil assembly where it was easier to move around than when it is flat against the frame.  Once I got the coil into the base correctly I was able to snap everything together and the tacky glue still has tack to seal the dome to the frame.

So as of now, seven of the original eight drivers are ready to go.  The one 8 inch driver needs to be replace. Both crossovers need to be recapped (I have Dillen's kit for those).  I will make sure the inductors on the crossover PCBs are securely mounted.  After that I should be able to give the speakers a listen.  The other tasks will be cosmetic - restoring the look to the cabinets, maybe repairing the scratches to the midrange/tweeter housing trim and possibly (long shot) restoring the missing top grill panels.  I'm not overly concerned with the grill covers as others have pointed out these speakers look good with the covers off...but if I find some.

I plan to start on the crossover recap tomorrow.

Søren Mexico
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Congrats John Good Work

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

sonavor
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Thanks Søren.  Here is a picture of the two sets of tweeter and midranges for the MS150.


Rich
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Rich replied on Wed, Apr 18 2012 6:35 PM

sonavor:

Success. 

Congratulations and well done.  I get to call you a "steely-eyed missileman" yet again.


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