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What´s Wrong With My Rick´s Pickup?

My 1940s Rickenbacker Bakelite lap steel (B8-model) is equipped with the then state-of-the-art pickup type with horseshoes.
It had been dormant for a while and when I took it out of the box I was disappointed by its tone. Had the rick not always been one of my best sounding steels? I had no explanation for that except that memory does not serve very well particularly when it comes to remembering a certain tone. But it also seemed very low in volume and that I could not explain at all. It was unlikely that something was broken, in which case there would have been nothing coming out of the guitar.
Was something deteriorated with time? Caps? Unlikely. Magnets? Never heard of it, that´s why they are called permanent magnets. I browsed the web and stumbled over it.

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Permanent Is Relative To Time

Little did I know that "permanent" is a relative term, it is relative to a certain time slot. Now by today´s perception of a magnet one would have expected that the permanence (or remanence in this case) was life long, and it is - but not our lifetime, rather the magnets´ lifetime.

To cut it short, back in the 40ies there was no material known to have any magnetic remanence anywhere near today´s magnet materials. For the Rickenbacker horseshoes they uses cobalt steel which was steel doped with cobalt to give it better magnetic properties. Cobalt steel has a magnetic half time (the timespan during which it looses half of its magnetism) of 50 years so I read (this is disregarding any additional demagnetizing sources like the vicinity of other strong magnets [like a loudspeaker] or mechanical shock).
My horseshoes would therefore have their best years long behind them and this became apparent just recently.

However, the horseshoes left the factory totally nonmagnetic (with their domains randomly oriented) and were magnetized lateron. This procedere has, by the way, never changed even today for all magnetic materials.

The upshot was, that my horseshoes had nearly lost their magnetic properties and needed remagnetizing.

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The "Official" Method - Using A Magneto Charger

Some more investigation on the internet revealed that materials like that can successfully be (re-) magnetized if they are exposed to a strong external saturating field that aligns their magnetic domains evenly. This task is usually accomplished  with a strong DC electro-magnet. That is the way it was done back then with very crude machinery such as this.

Although soon much better magnetic material was found like Alnico, Rickenbacker seemed to adhere to their horseshoe models for another decade or so (probably because they had coined a legacy tone...).

Later (much stronger) material cannot be magnetized with a simple electro magnet appliance. Those call for appliances that are more elaborate and potentially hazardous.

Today those technically antique appliances are only used for remagnetizing magnetic devices made within a certain narrow time slot. Vintage cars used to have an ignition system consisting of an array of horseshoe magnets made of weak magnetic material that had to be recharged periodically, so some Bosch stations might still have them.  A good magneto charger is available as D.I.Y. project by John Rex. A more contemporary approach may be pursued using the appliance shown by Rod Elliot. Let´s contemplate making one.
 
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Does Building A DC Magnet Charger Pay?

A device like that has to fulfill a couple of requirements.

• It has to deliver substantial momentary Flux, determined by the product of windings and current through them (ampere-turns)
• the iron yokes have to be of substantial diameter to guarantee that the to-be-magnetized material is saturated before the yoke is.
• the iron parts have to be made of a special quality material that does not store magnetism itself (remanence).
• it consumes a lot of copper wire of suitable length and diameter.

Despite its technical simplicity, all in all a pretty costly device and very heavy, way over the top for a single job. It is questionable whether this effort pays for just remagnetizing horseshoes. You can buy them, but buying a device that can do this is not cheaper. So this possibility phases out it you are not in the business of re-magnetizing.

Some aftermarket pickup makers like Lollar and Rick Aiello still use those electro magnetic devices and they do the job for you professionally for moderate fees. So if you are in need, don´t hesitate and save yourself a lot of potential trouble.
However, this was not an option for me since I live too far away.

Later I found a Bosch car repair center that still has a magneto charger, but I found a workaround.

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Using A Permanent Magnet That Can Be Switched Off (Magnetic Base)

In the meantime I had explored other avenues...
Where does magnetic flux come from?

• electric fields
  
• permanent magnets

Since today´s permanent magnets (made of rare earth materials, such as Neodym), some guys have arisen to the possibility of "re-charging"horseshoes with other permanent magnets. Denny Turner from Hawaii has made a fine art out of this and I am obliged to many thanks to him for clarifying some stuff. Those magnets produce way enough flux to saturate the wee old cobalt-steel horseshoes.

While this does basically work (the horseshoe makes no distinction to where the magnetic field comes from...), it bears some potential pitfalls.

Unlike an electro-magnet, the permanent magnet always has a field, it cannot be turned off. This means that upon removal of the now remagnetized horseshoes, some of the newly acquired remanence might be removed again. At least, some domains might be disturbed again if the two magnets were not separated perpendicularly with great care, which would cause an uneven magnetic flux density through the strings and thus imbalance in the picked up strings. So, the chance persists to make some damage after the re-magetization process.

But wait - there are some permanent magnets you can switch on and off - the magnetic base!

Since I have many of them in the work (they use them on all sorts of positions on the lathe) I borrowed the strongest looking one and made some experiments with it.

It appears that switching them gradually off just gradually short-circuits the magnetic field inside the iron yoke without making any funny things with the external field (such as N/S changes). I verified this with a compass needle.

I removed the horsehoes from the guitar according to the info on Rick Aiello´s page (well known boutique winder for steel guitars). They hardly picked up a screwdriver.

I put the horseshoes on the magnetic base over night (side by side) after determining their polarity with a compass needle and occasionally gave them small blows with a hardwood dowel as suggested on the site mentioned before.

Although I cannot measure the strength of the resulting (now hopefully permanent) magnets, they appear comparably much stronger now (attach well to my vise), so there is no point of measuring this either. Back in the guitar, this sounds like I remember it, thundering and sweet. I observed no irregularities in the magnetic field, such as an impaired string balance.

If the kind reader contemplates to use this method, I suggest to read the general guidelines for removing and installing horseshoes by Rick Aiello and the magnet handling precautions written by Denny Turner first. The author is not responsible for any damages resulting from applying this method.