Bang & Olufsen SP-12 cartridge/stylus "fix"?

[audiodummy]

I have a B&O SP-12 cartridge and stylus and it was acquired broken. This is for a Beogram 3000 but I forgot the exact submodel, thinking it's 5211.

The cantilever seems to be permanently attached into a cross shaped piece of metal that's apparently permanently stuck inside the "stylus replacement unit" which includes the top plastic shield and a metal shield that goes around the cartridge - which has four prongs that seem magnetic. When I slide this unit over the cartridge, the cantilever still seems very limp and collapses under the weight. I'm guessing the magnetic field on the prongs should sort of attract the cross shaped piece of metal, somewhat strongly, so that it won't collapse under the mass...

How strongly should the cross be attracted to the "magnetic" prongs? Should they "touch" that cross that the cantilever attaches to?

Based on this information, is this cartridge/stylus unit repairable? Should the prongs be magnetic? How strong should the magnet be?

I can't seem to find much info about this, best I see is https://www.vinylengine.com/turntable_forum/viewtopic.php?t=16930 ...

Thanks!

 

[Montycat]

I might be able to help. I have an SP-12 around here somewhere (that I have no need for) but it's late so will look at it some other day.

 

[audiodummy]

I'm still hoping I can understand the mechanism enough to repair it...Keeping my fingers crossed.

As far as I can tell (very poor ASCII art)

Stylus assembly:
. . . . . . . . _____________________
._____________/ |
/ . . . . . . | |oo
___/-----------X | Cartridge inserted here
V . . . . . . | |oo
. . . . . . ---------------------------
where V is the diamond needle.

The X is the cross piece of metal, and the oo's represents a hole for the protrusions that come out of the cartridge, and each o is for a point on the X. As far as I know this means this is a "moving magnet" cartridge though the magnet is actually stationary. I would guess that two of the protrusions from the cartridge should be a magnet, and the other two should be neutral for the electromagnet pickup... but I don't know much about the design of cartridges to make a good guess. However all four of the protrusions seem to attract the housing as I slide the stylus assembly onto the cartridge, which is a bit strange...

The holes for the protrusions in the stylus assembly *seems* deeper than the protrusion length, so the protrusions seems to not be able to touch the the X, which means an air gap and thus makes no sense - the magnets would need to be extremely strong to be able to hold up the (balanced) mass of cartridge/arm. As it is now, there's no pushback on the cantilever, any weight, even 1g (as far as I can tell; I tried to balance the arm to no mass at setting "0" but then merely moving it to "1" would collapse the cantilever) is too much.
I would guess two of the X arms need to actually attract/touch to the magnet and due to ferromagnetism would now be the magnet to tickle the "sensor" protrusions which does not need to touch, and probably shouldn't. But this is a guess, maybe all of them should not touch so that it has the most articulation.

All new to me...

 

[savatage1973]

Suspension failure is a known issue with B&O carts--do some research. I believe there is a guy out of Germany that can/does rebuild them, but it isn't cheap. Soundsmith also does some work on them, but I don't know to what extent, but they also do offer their own line of replacement carts--again, not cheap. I know people that have purchased NOS B&O carts that have failed almost immediately, so no guarantees there, either. FWIW

 

[audiodummy]

Ah... Thanks for needlestein, this was the bit of info that I needed. No, I don't have the "bullet casing" assembly taken apart further than removing it from the cartridge yet, but what you say makes sense. It sounds like this thing was not designed to last a long time (suspension separating from the microcross), which is a pity.

Time to see if I can carefully open this thing up some more.

 

[audiodummy]

Are all the pieces of the casing glued together, or is it press fit ... which I'm starting to think is how the pieces are held together. Looks like the "clear" plastic tip probably has 3 plastic prongs that protrude and friction fit into the "gray/silver plastic" that also has the 4 holes for the magnet prongs ... and the press fit also sandwiches the metal casing together.

Well, as you say, even if I break that plastic, so long as I glue the microcross back to the suspension, then it should still work just fine. I just worry I get the "camber" angle (excuse the car alignment caster/camber/toe terminology) correct which would make records sound very weird if it's wrong.

Thanks again.