Remagnetising, RWRP'ing and cleaning vintage Simeto pickups

[bpf8hz]

hello world

I've recently got my hands on two very nice guitars straight outta Deutsche Demokratische Republik: Musima 1657 and Eterna. Other than great looks and feels they've got one more thing in common - the original Simeto pickups. It was a pleasing (personal) discovery that those pickups are, in essence, a variation on the P90 formula. I won't dive too deep into the details as I really don't have them right now, but later I'll try to write something about them along with some RLC measurements (don't have a gaussmeter, unfortunately). Some quick facts (regarding the Eterna 3-pickup set), just in case I don't get around to it later:

• Pickups are top-mounted, each cover is slightly lower/higher than the other (neck < middle < bridge);
• Tiny screws are used as pole pieces;
  
• Bridge: 8.70K DCR;
  
• Middle: 8.35K DCR;
  
• Neck: 7.53K DCR;
  
• 2 bar magnets on each side of the bobbin;
• The bobbin can't be easily separated from the baseplate;
• All three conductors (coil start, coil end, baseplate/cover/shield) can be easily separated from each other by cutting the stock shielded wire and unsoldering from a holding clamp on the baseplate;
• The coil itself is not much larger than a regular strat coil;
• Pickups don't seem to be wax- or something-potted;
  
• All pickups seem to be the same polarity;
  
• They sound P90-esque, they sound great!
  

And some quick photos:

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Back to the topic now.

Question numero uno: how do I remagnetise these paired magnets properly? I remember reading something about it in this thread. Do I understand it correctly that I need to press a neodymium magnet to the attracting surface of a bar magnet and hold them together a bit? It also seems that it should not necessarily be the attracting side - the bar magnet (as the weaker one) would change its polarity, then. Though one could just flip the magnet...

I've got some round & thick and square & thin neo magnets that should do the trick. However, I don't quite get it regarding which side these barmags need to get remagnetised, and I really don't understand how should the magnetic pole sides be oriented relatively to the bobbin; the magnets being stacked in pairs doesn't help as well. Could someone sketch this process for a graphical representation of what to do, pretty please?

As far as I understand, regular P90s have the magnetic poles on the horizontal sides (if that makes any sense), whereas these Simeto barmags seem to have their poles on the vertical sides?..

By "poles on the horizontal sides" I mean the following:

SPOILER: Click to show

How should the poles be properly oriented on Simetos, then? Here are some photos that (hopefully) describe the situation on stock pickups:

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Question numero dos: I want to have the neck pickup RWRP'ed, so that B+N would be humbucking. Swapping the leads is easy; how should the magnets be repolarised/remagnetasied/reoriented and installed to the pickup relative to question number one, then?

Once again, a graphical representation would be VERY welcome!

Question numero tres: any ideas on how the baseplate cleaning would go (or would better be done)? As mentioned before, I can't really separate the bobbin from its baseplate, so the only option is to clean the pickup guts as a whole. I use Citranox solvent to clean all the furniture, it does a decent job without any (obvious) undesired effects. Right now I'm thinking of the cleaning process this way:

1. Put the pickup in an ultrasonic bath with Citranox solvent, let it do its job;
   
2. Soak the pickup in isopropyl alcohol to neutralise and get rid of the remaining solvent;
   
3. Profit!

I don't want to use the drying oven or whatever that thing's called, as A) isopropyl alcohol would dry on its own relatively fast and B) I don't have much confidence in the material the bobbin's made of. And it's more than half a century old by now, too!

Any ideas on whether such a process would affect the pickup (or the coil in particular) in a negative way? Perhaps there are better/alternative ways of cleaning the thing?

Stuff I'd like to clean up (this one would probably require some sanding as well):

SPOILER: Click to show

I'd like to sincerely thank everyone who's managed to read this post till the end and give it a thought!

[tubejockey]

Cool pickups.  I would not use an ultrasonic cleaner, as you are more likely to vibrate a coil until it breaks.  Those look like they have a good patina on them, but overall not too rusty.  I would probably leave them alone as long as they work.  Any remaining flux on them is so thoroughly dried up by now you could probably chip it off with a chopstick, but isopropyl alcohol will soften it if allowed enough time.  

[perfboardpatcher]

Hi Bpf8hz,


Nice presentation!

So if I understand it well you're saying that the pickups sound great but are lacking in output level?

Those magnets look like ceramics to me. They are not in contact with the iron core of the pickup which means less magnetisation of core and strings.

So I have been looking for a kind of magnet(s) that could be mounted against the core and which could fit inside/underneath the pickup.


Have you considered neodymium ring magnets like these ?

[bpf8hz]

Hi folks, sorry for the late reply, got too much something on my plate lately.

May 14, 2024 21:26:26 GMT -5 tubejockey said:

Cool pickups.  I would not use an ultrasonic cleaner, as you are more likely to vibrate a coil until it breaks.  Those look like they have a good patina on them, but overall not too rusty.  I would probably leave them alone as long as they work.  Any remaining flux on them is so thoroughly dried up by now you could probably chip it off with a chopstick, but isopropyl alcohol will soften it if allowed enough time.  

Yeah, I've also figured using an ultrasonic cleaner would be suboptimal (especially considering the fact I've broken a coil tail <-> pickup lead connection while getting the tape off before). I decided to go the Citranox bath route in the end:

1. Let the coil (still on its baseplate) soak in Citranox solvent for some time (I left it for about an hour or two as I had to clean up some guitar hardware simultaneously);
2. Scrub off some softened goo with an abrasive brush, put the coil back in the bath;
   
3. Put the coil in a tar filled with room temperature water to "wash off" some leftover chemistry out there;
   
4. Let the coil soak in isopropyl alcohol for a bit to neutralise all the nasty stuff and make the drying process manageable;
5. Let the coil dry on its own for a while.

That seemed to do the trick! I'll probably go for round 2 sometime soon, as I want to free the baseplate in particular from any corrosion/whatever as much as possible. The coil itself hasn't been damaged in the process, and my DCR readings are still the same, so that's a relief.

I've also cleaned up the magnets by soaking them in isopropyl and using the same abrasive brush afterwards. That glue was... tough. It seems to have melted with the coil tape, making the matters worse, and wouldn't come off the magnet easily. It all looks good now, though:

SPOILER: Click to show

May 30, 2024 1:35:27 GMT -5 perfboardpatcher said:

Hi Bpf8hz,


Nice presentation!

So if I understand it well you're saying that the pickups sound great but are lacking in output level?

Those magnets look like ceramics to me. They are not in contact with the iron core of the pickup which means less magnetisation of core and strings.

So I have been looking for a kind of magnet(s) that could be mounted against the core and which could fit inside/underneath the pickup.


Have you considered neodymium ring magnets like these ?

Well, the output level is actually quite good, seems to be in the regular P90 ballpark. I'm not sure about the material used to produce those magnets; somehow I doubt that ceramic magnets were already widely used in the DDR throughout the sixties. Maybe it is more clear now that I've got some pics of those magnets after cleaning?

Also they really don't seem to be in contact with anything, but I'll comment on that in greater detail in my next post.

The neodymium ring magnet idea is cool, but with this project I really want to preserve the original design and parts as much as possible. Eastern bloc guitars haven't really been treated well since their inception, and some of the design choices are rather fascinating.

In other words: with these pickups I want to 1) restore their magnets' charge by recharging them (a reversible modification that does not go in the way of authenticity) and 2) make one pickup RWRP to get some free lunch (doesn't really affect the pickup's performance & gives some hum cancelling). So changing the magnets' charge/orientation is OK in my book this time; changing the magnets themselves (unless those go FUBAR) is NOT OK.

A neat solution for another project, however

[ms]

Why do you think the magnets need to be re-magnetized if the pickups sound good and have enough output?  I also do not see what they could be except ceramic (which was widely available by the late sixties) and I do not see why they would lose their magnetization.  I think the orientation is like the P-90, with an important exception.  That is, the coil fits between the magnets, requiring strong magnets, and a lot of steel in the core of the coil.  (I am assuming that the screw pole pieces screw into a steel bar that forms the core of the coil, and that the two inward pointing magnets magnetize that bar as the two magnets touching the screws of a P-90 magnetize them.)  The disadvantage is that there would be high eddy current loss in the core, and so the pickups would not be very bright.

[perfboardpatcher]

Bpf8hz,

Can you tell me whether those two L-shaped pieces at the the bottom of the pickup are ferro-magnetic or not?

My guess is they are. You were wondering about the orientation of the magnets. In case of those bottom pieces being ferro-magnetic it could be that one of the poles - whether S or N - of the magnets is supposed to point to them and not to the pickup core.

Isn't it a matter of what works best. Mount the magnets in a certain way and check magnetic pull with a screw driver. The stronger the pull the better.

[bpf8hz]

Ugh, I'm still barely able to find some time to post here, but (finally) here goes!

So I said that I'd elaborate on the magnetic part of those pickups, and here's what I've found out experimentally:

• Magnets seem to be glued to the baseplate, to the tape surrounding the coil wire and to each other
  
• Magnets have their poles spread vertically: up is S, down is N, same on both sides of the coil
  
• Excessive amount of glue seems to be used to hold the magnets in place with each other as those repel each other (due to having the same magnetic pole orientation)
  

Graphically it looks something like this (sorry for my garbage drawing skills):

SPOILER: Click to show

That raises the following questions:

1. Should the magnets on one side be reoriented relative to each other, so that they would attract?
   
   SPOILER: Click to show
   
   
   
2. Maybe each pair of magnets should be reoriented relative to another pair?
   
3. IOW: what is the most optimal way to put the magnets back on the pickup? Or maybe the stock configuration is already "proper"?
4. If the stock magnet alignment is OK, wouldn't that be bad for, well, magnets? Wouldn't having the same polarity & forceful coupling (they're glued together) be bad for their magnetic characteristics?
   

If the answer to question 3 is "it can be considered proper as-is", then RWRP'ing seems to be pretty straightforward: flip all the magnets upside down, swap the leads, done.

If, however, a different alignment is chosen, then I'd like to ask for advice on RWRP'ing the pickup. Having not one, but two magnets on each side of the coil seems to REALLY confuse me.

I really want to get the magnetic part right, especially if I want to successfully reassemble this 12-magnet bad boy

(check out the bobbins, cool stuff; these came from a semi-hollow Musima 1657)

SPOILER: Click to show

Jun 6, 2024 11:51:58 GMT -5 ms said:

Why do you think the magnets need to be re-magnetized if the pickups sound good and have enough output?  I also do not see what they could be except ceramic (which was widely available by the late sixties) and I do not see why they would lose their magnetization.  I think the orientation is like the P-90, with an important exception.  That is, the coil fits between the magnets, requiring strong magnets, and a lot of steel in the core of the coil.  (I am assuming that the screw pole pieces screw into a steel bar that forms the core of the coil, and that the two inward pointing magnets magnetize that bar as the two magnets touching the screws of a P-90 magnetize them.)  The disadvantage is that there would be high eddy current loss in the core, and so the pickups would not be very bright.

Thanks for the insight! Would be nice to hear your thoughts on the topic on magnets' orientation & operation with the context I've written above.

Regarding the re-magnetising thing: it seemed to me (from reading the thread I've linked in the OP) that magnets in general lose their pull over time. If people hunt for "aged" pickups and their sounds, the I reckon the difference between a new magnet vs. 50+years-aged magnet in the same pickup is quite noticeable. Given that, I'd like to "refresh" these Simetos so that they'd seem "as new" and I wouldn't have the need/urge/etc to open them up for the rest of the century.

Jun 9, 2024 2:42:41 GMT -5 perfboardpatcher said:

Bpf8hz,

Can you tell me whether those two L-shaped pieces at the the bottom of the pickup are ferro-magnetic or not?

My guess is they are. You were wondering about the orientation of the magnets. In case of those bottom pieces being ferro-magnetic it could be that one of the poles - whether S or N - of the magnets is supposed to point to them and not to the pickup core.

Isn't it a matter of what works best. Mount the magnets in a certain way and check magnetic pull with a screw driver. The stronger the pull the better.

I'm not quite sure what those L-shaped pieces might be. Are you talking about the part of the baseplate that's curved and goes inside the bobbin?

[ms]

Use the stock orientation; it works differently from other pickups but I think those guys knew what they were doing.  The orientation is not bad for the magnets, and so do not reverse one as you are considering above.  Alnico can have its magnetization changed easily (given the really strong magnets we have these days), but ceramic less so. (For example, speakers can be made a lot cheaper with ceramic than Alnico because, not only is it inherently cheaper, you need less of it to resist the demagnetization from the current in the speaker coil.)

To understand how these pickups work, let's first look at the more usual way.  There is a field in the pole piece(s) pointing along it.  This emerges from the pole piece and bends in order to circle around to the other end of the pole piece.  Thus there is a field component along the string pointing in opposite directions referred to over the pole piece.  Long thin structures magnetize primarily in the long direction, but in this case, (write again for emphasis) the direction of magnetization reverses over the pole piece.  It is this reversal  that results in a field component from the string that points through the coil. (Picture the fields of two oppositely pointing thin bar magnets end to end pointing in opposite directions and spaced a bit apart and see that the the components perpendicular to the "long" direction add and are significant only near the pole piece.)  Move the string, and the field through the coil changes because it is a function of distance from the string.  (OK, it is really a bit more complicated than that simple analysis.)

Now back to these pickups.  The magnets induce magnetization in the string that point in opposite directions, and similar to above there is a field from the string pointing through the coil over the pole piece resulting from the change in direction along the string.  This change might be more gradual in this case and extend over a larger length of string, and so I am unsure about the efficiency of this method, but apparently it works well.

[perfboardpatcher]

Jun 10, 2024 5:49:22 GMT -5 bpf8hz said:

SPOILER: Click to show

Jun 9, 2024 2:42:41 GMT -5 perfboardpatcher said:

Bpf8hz,

Can you tell me whether those two L-shaped pieces at the the bottom of the pickup are ferro-magnetic or not?

My guess is they are. You were wondering about the orientation of the magnets. In case of those bottom pieces being ferro-magnetic it could be that one of the poles - whether S or N - of the magnets is supposed to point to them and not to the pickup core.

Isn't it a matter of what works best. Mount the magnets in a certain way and check magnetic pull with a screw driver. The stronger the pull the better.

I'm not quite sure what those L-shaped pieces might be. Are you talking about the part of the baseplate that's curved and goes inside the bobbin?

Bingo! To me it would make sense if those two baseplates were made of iron to avoid the situation were one has an air gap between magnets and Core. 

[bpf8hz]

Okay, it looks like I'm finally getting close to the finish line with these. Gotta get those two fancy semi-hollowbody guitar pickups assembled first in order to continue messing with it at the workshop and finally get it off my todo-list. I've prepared the bobbins and polished the baseplates; I'll post another batch of photos once I get things sorted out.

Just a couple of quick questions, though:

• The practical one: what would be the "better" way to glue magnets to the baseplate? I'm mostly concerned about the type of glue to apply there. I have some superglue and some "epoxy+something" two-component thing on my hands. Would superglue be fine for the purpose of keeping two magnets of the same polarity fused together while being firmly attached to the baseplate, or should I get my hands dirty with that epoxy-thing glue (which I really don't want to do TBH)? Should I bother with keeping the magnets in contact with the baseplate (== applying glue on the edges, not on the sides), or maybe that doesn't matter too much? I'm thinking the latter's true, as it's the magnetic field that matters, not the magnet's contact surface with the baseplate.
  
• The theoretical one: I've stumbled upon a post on SD forums where someone basically claims that if one glues two magnets together first and only then recharges them (with e.g. neo magnets), then the resulting combination would be more like a "single" magnet - as opposed to charging individual magnets first and gluing them together with same polarities later on. Could anyone comment on this? I think that would kinda work that way if the magnets were welded together, but it wouldn't be the case with the magnets glued to each other, as those would still be two separate pieces of material pulled together mechanically.