Pickup Magnets

[THRobinson]

Hey guys... starting to build a pickup winder and seen a lot of vids about making them etc, and seems pretty straight forward for the most part.

I was wondering however, let say you had to recreate a pickup, or you had an old one missing a pole, etc... how do you know what magnet was used? Alnico I, II, III, etc... like, let's say someone handed you a handful of single coil pickup poles and asked you what they were, how do you tell?

 

[El Dunco]

Colour (ceramic is always black, alnico looks like metal), sometimes the finish (shiny vs rough) and conclusively, the gauss of the magnet when charged if you want to be sure what type of alnico it is.

 

[jeremy]

telling different types of alnico apart is hard since they basically all look the same. a5 and a2 are probably the most common, and if fully charged, a5 will be noticeably stronger

 

[freefrog]

Measured inductance VS magnetic strenght can help. The more iron there is in an AlNi(Co) alloy, the more inductivity it will bring while the measured Gauss / Tesla will drop.

A3 = 60% of iron. Max inductance, min mag strenght.
A2 = 55% or iron.
A4= 52%.
A5= 51%. Max mag strength and min inductance compared to A3 among well known recipes.

Then there's less used alloys like A6 (with 49% of iron), A8 (with 29 or 34%? I don't remember)...

Such small differences in proportions can affect the results in a noticeable way.

Reason why a test will be reliable only if it compares pickups with the same wind and hosting a same mass of magnetic material charged the same time in the same way...

The only way to know for sure remaining metalurgical analysis, IMHO. YMMV.

 

[eclecticsynergy]

Measured inductance VS magnetic strenght can help. The more iron there is in an AlNi(Co) alloy, the more inductivity it will bring while the measured Gauss / Tesla will drop.

A3 = 60% of iron. Max inductance, min mag strenght.
A2 = 55% or iron.
A4= 52%.
A5= 51%. Max mag strength and min inductance compared to A3 among well known recipes.

Then there's less used alloys like A6 (with 49% of iron), A8 (with 29 or 34%? I don't remember)...

Such small differences in proportions can affect the results in a noticeable way.

Reason why a test will be reliable only if it compares pickups with the same wind and hosting a same mass of magnetic material charged the same time in the same way...

The only way to know for sure remaining metalurgical analysis, IMHO. YMMV.

When gauging inductance in a magnet do you measure its effect on the coils, or directly measure the metal itself?
And if measuring the metal directly, does one need to account for size/weight/shape, or is it constant regardless of those?
I finally got a meter that can read inductance.

 

[freefrog]

Well, an inductor (a coil) being necessary to induce some current, the measurements that I evoke are necessarily done on the coils of pickups.

The best thing to do IMHO is to measure the inductivity of a coil itself (as an air coil) then to see how its inductance changes according to the core material(s) used, leading the resonant peak to change. Here is an example that I shamelessly borrow to Dr Scott Lawing @ Zexcoil:
https://images.squarespace-cdn.com/c...g?format=1000w

If you have a DMM able to read inductance, keep in mind that it varies with frequencies and that low testing frequencies are better for guitar tranducers (any test done at high frequency being prone to give inaccurate results because of Foucault currents).

And keep in mind mutual inductance: it's normal to read a higher inductance for an humbucker as a whole than a simple addition of the inductive values of its coils separately.

EDIT - Was busy yesterday, so I can complete my answers only now.

let's say someone handed you a handful of single coil pickup poles and asked you what they were, how do you tell?

In this case and on the basis of tmy previous message: I would use a single coil with plastic bobbin (as it's the case for some Fender Strat PU's and many cheap clones) deprived of its initial magnetic poles. I would measure the inductance of its coil without poles then with various rod magnets. I'd take in account the measured weight and Gauss / Tesla of these rods. By correlating all these infos, I would have an idea of the alloy used... but just an idea, since only lab analysis would give me a reliable answer.

That being said...

-rod magnets are meant to be A5 most of the time. For such tiny cylinders, other alloys are way less commonly used even if first Strats from the fifties had A3 and if winders have started to use other alloys (A2, A4) decades later;

-this idea doesn't help me. I'm pretty sure that a L Series Strat periodically tested here hosts PU's with A5 rod magnets when I see their inductance relatively to their DCR... but our teslameter reacts in a special way with these pickups: their magnetic field has simply not the same strength nor the same shape (diffusion) than with modern generic A5... so, I'd have no way to reproduce these pickups faithfully when it comes to materials, anyway. I'd have to "tweak" the recipe with modern components.

FWIW.

 

[AlexR]

Destructive testing is one of the only true ways.......even gauss sometimes can be a little inconclusive as there are so many overlaps and differences with where the source material comes from.

For the purposes of you as a new winder - you are not going to be replicating anything for the first few months/years of winding. Your biggest achievement initially will be getting to your desired turn count without breaking the wire. Then it will be making a neat pickup coil after you do manage to get the wire on a bobbin reliably. Then after that will be learning how the wire pattern on the coil can be used to make tonal outcomes.
The magnet type will be less important until you have these down.....much less trying to find an accurate alnico grade to something lost or in a specific wind. And by that time you will have worked out what works for you rather than trying to copy something else.

As to something missing a pole.......well if its a humbucker then these are not magnets, and if its a strat then odds on you'll destroy the pickup trying to re-install something - strat poles for the most part an integral structural element that cannot simply be 'replaced'.

 

[GuitarDoc]

Wow, Freefrog, that's some great info...the iron content relative to the inductance and strength of the most used types of magnets.

 

[freefrog]

Simply glad if my rambling helps, Doc.

Now, it would be less easy for me to ramble if there wasn't great online contributions from various winders like Scott Lawing. His blog is a precious source of reliable information IMHO.

 

[eclecticsynergy]

Well, an inductor (a coil) being necessary to induce some current, the measurements that I evoke are necessarily done on the coils of pickups.

Thanks for the clarification. I guess it should've been pretty obvious that inductance was induced, not intrinsic. D'oh!
What confused me was the correlation with iron content.
But I realize now that inductance is the effect on a coil, and the inductivity of a magnet is what causes it.

 

[Clint 55]

That's pretty cool, freefrog. What instrument do you use to measure inductance? And have you ever measured the inductance of 1 pickup with all the magnets?

 

[freefrog]

We use various inductance meters : Tonghui THD 2811D, Wavetek 27XT, Extech...

And yes, the routine here is to measure the inductance of pickups with different magnets, with and without "magnetic circuit" and so on. Now, testing a pickup with "all the magnets" would be very long, since a generic name like "AlNiCo" is applied to many recipes, varying with foundries and eras.