Magnet Source/Type/Magnetic Properties

[Helmholtz]

Charts i have seen show A4 is lower than A5.

I don't think anybody indicated that A4 would charge higher than regular (anisotropic or oriented) A5. In fact A4 has the lowest remanence of all alnicos, but it has high coercivity. In bar shape it can be charged up to 600G / 650G measured exactly at the center of the pole face - similar to A2. A5 charges up to 700G / 850G.
Cylinder shaped magnets generally charge higher than bar magnets.

My question is are the A4 magnets being sold just a A5 that is not fully charged?

Never heard of something like that.

[Antigua]

Since I don't have a gauss meter I can only check the strength of the magnets with a screwdriver [or something like that] . The A4 are weaker then the A5 so I just assume they are indeed A4!

The WT10A costs only $100 on Amazon. I think it's a good idea to have a magnetometer on if you care what kind of magnets you have on hand, because hanging paperclips and such methods is really hit or miss. That will distinguish AlNiCo 7 or 8 from AlNiCo 5, and AlNiCo 5 from the lower grades no problem, but in some cases you can even tell apart AlNiCo 2, 3 and 4 based on the slight difference of Gauss strength.

Partially degaussing AlNiCo is tricky, because the opposing charging field has to be very precise the alter the remnant flux by such a fine amount. It's much easier to fully charge them to one polarity or another. And when they are partially degaussed, they are less stable, and prone to lose even more magnetic strength, so it's very unlikely that anyone is dealing with partially degaussed AlNiCo, even if it's technically possible.

[Brian W.]

Every A4 I've seen will charge lower than an A5 & they don't sound the same . .I don't think magnet strength tells the tale . I find Alnico 5 has a kind of scooped tone with a fuzzy top end & an Alnico 8 has more mids .

HHHmmmm...I need to try a few A8 's !

[mozz]

"Partially degaussing AlNiCo is tricky, because the opposing charging field has to be very precise the alter the remnant flux by such a fine amount. It's much easier to fully charge them to one polarity or another. And when they are partially degaussed, they are less stable, and prone to lose even more magnetic strength, so it's very unlikely that anyone is dealing with partially degaussed AlNiCo, even if it's technically possible."

Now this is contrary to what i have just read within the last week, either a magnetic website or was a college or science pdf or something of that nature. If i can find the page i will link. It stated a slightly degaussed magnet will be more stable than a fully charged magnet. It was either 5% or 10% and the set of humbuckers i just made got it almost exact 5% down when i put it on a old cassette demagnetizer with a wooden block for a spacer. It must have been fresh in my mind so i think it was 5% down from 100 is more stable.

One thing i did notice but didn't really pursue more was, when fully charged, one pole was higher reading than the other. After knocking it down 5% they were much closer to each other than before. Will have to keep my eye open and see if this happens a lot or is rare.

Currently tearing apart import humbuckers, tossing the ceramics and rewinding them. 5000/5000, 4900/5100, 5200/5400 winds, measuring air coils (about 1H) and whatever else. Some bobbins have .195 slugs, some bobbins have legs instead of spacers, some slugs were beveled on one end yet were inserted all different directions with no set pattern.

You can buy these green sheets on Amazon, had to fill a order to get free shipping, about $8, here is a humbucker and the degausser (open E core?) transformer.

[Antigua]

"Partially degaussing AlNiCo is tricky, because the opposing charging field has to be very precise the alter the remnant flux by such a fine amount. It's much easier to fully charge them to one polarity or another. And when they are partially degaussed, they are less stable, and prone to lose even more magnetic strength, so it's very unlikely that anyone is dealing with partially degaussed AlNiCo, even if it's technically possible."

Now this is contrary to what i have just read within the last week, either a magnetic website or was a college or science pdf or something of that nature. If i can find the page i will link. It stated a slightly degaussed magnet will be more stable than a fully charged magnet. It was either 5% or 10% and the set of humbuckers i just made got it almost exact 5% down when i put it on a old cassette demagnetizer with a wooden block for a spacer. It must have been fresh in my mind so i think it was 5% down from 100 is more stable.

One thing i did notice but didn't really pursue more was, when fully charged, one pole was higher reading than the other. After knocking it down 5% they were much closer to each other than before. Will have to keep my eye open and see if this happens a lot or is rare.

That's true, when you first charge the, they're about 5% to 10% stronger, and then after about fifteen minutes or so they settle to a state where they remain indefinitely. That's what I mean by fully charged, since that initial high value is so short lived.

I got some information that might have been incorrect, according to https://www.pafhumbucker.com/paf-pickups-magnets.html " In order for Alnico to be most stable it should be fully saturated." But just now I came across some info that makes a compelling case that the magnet is actually more stable after degaussing https://e-magnetsuk.com/alnico_magne...teristics.aspx:

This method of tuning is sometimes also known as “knocking-back” – you should always fully magnetise then weaken rather than just weakly magnetise because knocking back demagnetises the zones (domains) of the magnet that have the worst Hci values leaving the domains that are harder to demagnetise leaving a more stable magnet which is better at resisting being demagnetised accidentally (which is why knocking back is also known as “stabilizing”). Some designs will deliberately request a stabilization to provide a designed-in lower magnet performance but with an improved resistance to demagnetisation by external magnetic fields.

TL;DR: when you degauss the magnet, the weakest domains are the first to go, thus what remains are more stable domains. That makes sense to me. And that also explains why it loses strength after the initial saturation; it's the weakest domains losing their polarization.

There is other good info on that page also, such as the section that talks about the importance of AlNiCo requiring at least a 4:1 length to diameter ratio in order to have optimal strength and stability. There are some pickups out there using AlNiCo magnets that have ratios below 4:1.

There is a method of degaussing that's not too tedious; press two AlNiCos together, face to face. Each AlNiCo mutually loses about half it's charge, give or take. Even that method wasn't exactly fool proof, it would sometimes take me a few tries to hit a particular target. If you can get AlNiCo 5 down by a clean half, then it will have a similar flux density as AlNiCo 2 or 3, which is a useful outcome. Maybe with an electromagnet, a very specific voltage could be applied that that would be even better, but trying to do it with a neodymium is fairly difficult, IME.

[Brian W.]

" "There is a method of degaussing that's not too tedious; press two AlNiCos together, face to face. Each AlNiCo mutually loses about half it's charge, give or take. Even that method wasn't exactly fool proof, it would sometimes take me a few tries to hit a particular target. If you can get AlNiCo 5 down by a clean half, then it will have a similar flux density as AlNiCo 2 or 3, which is a useful outcome. Maybe with an electromagnet, a very specific voltage could be applied that that would be even better, but trying to do it with a neodymium is fairly difficult, IME." "

HHmmm......if that's the case then quite a few of my magnets have been quietly degaussing without my permission!

[Antigua]

" "There is a method of degaussing that's not too tedious; press two AlNiCos together, face to face. Each AlNiCo mutually loses about half it's charge, give or take. Even that method wasn't exactly fool proof, it would sometimes take me a few tries to hit a particular target. If you can get AlNiCo 5 down by a clean half, then it will have a similar flux density as AlNiCo 2 or 3, which is a useful outcome. Maybe with an electromagnet, a very specific voltage could be applied that that would be even better, but trying to do it with a neodymium is fairly difficult, IME." "

HHmmm......if that's the case then quite a few of my magnets have been quietly degaussing without my permission!

Face to face, like south against south or vice versa.

[Brian W.]

Face to face, like south against south or vice versa.

Face to face prevents any degaussing?

[Antigua]

Face to face prevents any degaussing?

Causes it.

[Brian W.]

Causes it.

O.K.....so stacking the magnets is a no-no. How about side-to-side?

[Helmholtz]

O.K.....so stacking the magnets is a no-no. How about side-to-side?

Actually stacking magnets along their magnetic axes with poles arranged N/S/N/S (unlike poles attaching) is one of the safest way to store magnets. Bringing repelling (like) poles close together causes demagnetizing. Also avoid letting the large flat sides attach and don't stick the magnets with their flat sides to steel objects (https://iopscience.iop.org/article/1...1/33/8/307/pdf).

[Antigua]

O.K.....so stacking the magnets is a no-no. How about side-to-side?

Face to face is not stacking, the magnets will repel if you press them face to face. Face to face means "south on south" or "north on north".

If you press two AlNiCo magnets together, defying their tendency to repel, they will mutually demagnetize.

[Brian W.]

My definition of "face to face" is putting the large flat "front & back" together [not the thin sides].

[mozz]

I don't think they would mutually demagnetize but what do i know. I would say they would even out. Wouldn't 75 year old P90's be all dead?

[Helmholtz]

I don't think they would mutually demagnetize but what do i know. I would say they would even out. Wouldn't 75 year old P90's be all dead?

Not quite clear what exact situation you are referring to. As has been said, pressing repelling alnico magnet poles together demagnetizes both magnets to some extend. Typically the stronger one (or the one having higher coercivity) remains the stronger one and the weaker one demagnetizes more.
Magnetization and de-magnetization are instant effects and the results depend on max field strength but not on time of exposure. (Repeating the procedure, though, often does produce some additional effect.)
For this reason the magnets in a P-90 don't lose strength over time. The magnets of P-90s from the 50s typically are not weaker than PAF magnets of the same age.
Also when you (dis)assemble a P-90 you will notice that the like inner poles actually lightly stick to the keeper. This shows that when finally assembled there is no more demagnetizing field.