Any idea what alloy Duncan uses on their keepers and polepieces?

[NateRS]

Hi all,

I have been winding off and on for the past few years (mainly humbuckers). I generally use either 1018 or 12L14 alloy keeper bars and have played around trying a mix of different alloys for pole screws and slugs (1018, 1022, 1215, 12L14, 1010) from Addictionfx, Mojotone, Philadelphia luthier tools and Microfasteners.

Anyways, recently I was testing out a bridge PAF style pickup I wound using about 5500 turns of 42 pe wire on each bobbin. I used a alnico 5 magnet and 12L14 alloy slugs, keeper and polepieces. I found the pickup to be very bright and somewhat sterile at first when testing it out in my Les Paul. On a whim, I swapped out the keeper and pole pieces for ones I had laying around from a duncan 59. I immediately notices a complete difference as the pickup no longer had the ice pick it had before and had a warmer all around sound to it.

Out of curiosity, I wanted to see if anyone had an idea of what alloy Duncan uses for their keepers and poles, so I can order some more? I would guess 1018 since it seems to be the most common but wanted to see if anyone knew for sure. Thanks

[David King]

You can make a crude guestimate of a steel's carbon content by touching it to a grinding wheel and looking at the sparks it throws off. Comparing sparks from known alloys with the unknown might get you pretty close but I've never tried to do this. Higher carbon steel sparks leave a short trail and then explode into very fine sparks. Low carbon steel has a coarse spark with a long trail and no explosion at the end. Other steel alloys can behave in confusing ways with a variety of colors so there's a lot one needs to experience first hand to get a handle on precise identification. It's low tech only requiring a $40 6" grinder so I'd think it was worth a try.
Here's a little primer on wikipedia: https://en.wikipedia.org/wiki/Spark_testing

[David King]

Note that the fellow who originated spark testing in 1909 claimed to be able to identify carbon content in steel to a .01% resolution, i.e. he cold tell the difference between 1018 and 1019. So it's possible.

[NateRS]

Note that the fellow who originated spark testing in 1909 claimed to be able to identify carbon content in steel to a .01% resolution, i.e. he cold tell the difference between 1018 and 1019. So it's possible.

Interesting, I've never even thought of trying that. I'll give it a try and see if it comes close to the other pole pieces I have. Thanks David

[copperheadroads]

Note that the fellow who originated spark testing in 1909 claimed to be able to identify carbon content in steel to a .01% resolution, i.e. he cold tell the difference between 1018 and 1019. So it's possible.

A local welder/Fabricator told me the same thing .

[Joe Gwinn]

Any soft steel will act the same magnetically in a pickup, because the magnetic path is mostly air.

Physically softer iron alloys are more conductive to both magnetic flux and eddy currents.

If it's a low carbon steel, as is likely, spark testing won't tell them apart.

The physical dimensions of the keeper bar and the holes for the screws will matter quite a lot, as eddy current loading (which will tame the high-frequency edge of the tone) vary as the square of the smallest thickness perpendicular to the magnetic flux. Another way to think of this is to imagine the eddy currents as a blurry image of the nearby coil - what interrupts the flow around this blurry image.

To make an accurate comparison of alloys, make a series of keeper bars of identical physical dimension, but differing materials, and try them one by one.

[Mike Sulzer]

Any soft steel will act the same magnetically in a pickup, because the magnetic path is mostly air.

That is certainly true in regard to the effects of permeability differences as they affect the inductance of the coil. It is easy to show that changes in the relative permeability have an effect for numbers on the order of a few, but all soft steel is above that, up in the range where it matters very little.

However, I do not think this argument works for the effects of eddy currents in the cores (responsible for most of the observed differences, I believe), or the spacer bar. The difference is that for the inductance the relevant path goes out one end of the coil out into air and back into the other end. For eddy currents in the cores, the path is simply around the cores, no air involved. I believe that a similar argument applies to the bar, although the situation is a bit more complicated. Thus I think these currents are sensitive to small changes in both the conductivity and permeability. And matter it does; measurements show that the dominant loss in a humbucker in the range where the ear is most sensitive can be from these currents, not from the resistance of the coil.

EDIT: I should add that the permeability affects the eddy currents in the cores because it is a factor in the skin depth: the currents tend to flow near the surfaces of the cores, depending on the frequency.

[David King]

Has anyone ever considered a laminated keeper bar? Not sure what that would accomplish or which way the eddies are circulating. It would be highly impractical if the whole length had to be chopped up like a carrot but a stack of perforated horizontal plates might be doable.

[Mike Sulzer]

Has anyone ever considered a laminated keeper bar? Not sure what that would accomplish or which way the eddies are circulating. It would be highly impractical if the whole length had to be chopped up like a carrot but a stack of perforated horizontal plates might be doable.

I think "vertical" plates would do it, Joe might know better. In any case, I think the bar is not as big an effect as the cores.

[Joe Gwinn]

I think "vertical" plates would do it, Joe might know better. In any case, I think the bar is not as big an effect as the cores.

If by "vertical" you mean that the lamination sheets are perpendicular to the plane of the coil, you are correct. The eddy currents more or less parallel the coil windings, and if the laminations are perpendicular to the coil winding, the eddy current is forced to circle in the thickness, not the face, of the laminations.

You are right that both magnetic permeability and electric conductivity matter for eddy current skin depth, but the skin depths of soft iron alloys don't vary all that much (excluding things like permalloy and mu metal).

[John Kolbeck]

Any idea why laminated humbucker cores isn't a thing? It seems like it would be a good way to achieve a unique result over what can be done currently with steel pole pieces.

edit: never mind, I found a detailed thread on the subject http://music-electronics-forum.com/t35164/

[Lollar Jason]

If you only need to test a couple of parts mass spectrometry is not very expensive. I have had alot of parts burned and I think we pay about $75 per test and youll find out exactly what the composition is. Lots of places that do it to select from.

[big_teee]

Hi all,

I have been winding off and on for the past few years (mainly humbuckers). I generally use either 1018 or 12L14 alloy keeper bars and have played around trying a mix of different alloys for pole screws and slugs (1018, 1022, 1215, 12L14, 1010) from Addictionfx, Mojotone, Philadelphia luthier tools and Microfasteners.

Anyways, recently I was testing out a bridge PAF style pickup I wound using about 5500 turns of 42 pe wire on each bobbin. I used a alnico 5 magnet and 12L14 alloy slugs, keeper and polepieces. I found the pickup to be very bright and somewhat sterile at first when testing it out in my Les Paul. On a whim, I swapped out the keeper and pole pieces for ones I had laying around from a duncan 59. I immediately notices a complete difference as the pickup no longer had the ice pick it had before and had a warmer all around sound to it.

Out of curiosity, I wanted to see if anyone had an idea of what alloy Duncan uses for their keepers and poles, so I can order some more? I would guess 1018 since it seems to be the most common but wanted to see if anyone knew for sure. Thanks

Did you try to isolate the added SD parts?
To see if it was the slug bobbin, screw bobbin, keeper, or all that effected the tone?
If you could isolate which part made the difference, then you would have less parts to analyze?
If you're using the ADFX baseplate?
I found it to be unusually bright, compared to other brands.
Also Bright can be good if you're adding a tone robbing cover?

On the laminated keeper?
Besides the added building complexity issues, If the tone is already too bright, IMO the laminated keeper could just make it worse.
T

[tedmich]

If you only need to test a couple of parts mass spectrometry is not very expensive. I have had alot of parts burned and I think we pay about $75 per test and youll find out exactly what the composition is. Lots of places that do it to select from.

These units by Bruker work great for identifying alloys using x-ray fluorescence

spendy but maybe a metallurgist friend will do you a favor

[Mike Sulzer]

If by "vertical" you mean that the lamination sheets are perpendicular to the plane of the coil, you are correct. The eddy currents more or less parallel the coil windings, and if the laminations are perpendicular to the coil winding, the eddy current is forced to circle in the thickness, not the face, of the laminations.

You are right that both magnetic permeability and electric conductivity matter for eddy current skin depth, but the skin depths of soft iron alloys don't vary all that much (excluding things like permalloy and mu metal).

Yep that is what I meant.

i am thinking that it does not take very much difference to be audible. Even untrained people hear differences in damping as a different sounding instrument. A guitarist or pickup maker listens a lot more and probably develops a high sensitivity to this.

Lokking here: Properties of soft magnetic materials

The relative permeabilities for some steels at low applied field levels are (steel, relative perm.):

1006 1530

1008 1486

1010 460

1018 790

1020 151

1030 241

There appears to be a significant variation, and not necessarily so easy to understand, but I think some of the audible differences would be significant.