Bill Lawrence quote on "decay" and its measurement

[kayakerca]

I have a 2 part question. I was reading a bunch of Bill Lawrence stuff today and was curious about the nature of the "decay" he referred to in the excerpt below from one of his articles and if it was something that was measurable by the hobbyist?

"I have measured the magnets of numerous and beautifully sweet sounding vintage strat pickups, and they have not lost any magnetism. The coils had up to ten percent tolerance in DC resistance caused by the tolerance of the coilwire and by the difference in tension at the coilwinder. This will have no influence on the sound of the pickup. One thing all these good sounding pickups have in common is they all have less than four percent decay. Three to four percent is the expected amount of decay due to core loss of fully magnetized Alnico V magnets. Any additional decay is caused by minute shorts or even semi-shorts in the coil. These shorts are extremely hard to detect. However, in the past five years I have developed a measuring technique to detect these shorts. If a coil is perfect, the pickup will sound great. A thousand turns, more or less, have very little effect on output or sound. There is no difference between layer or scatter wound, hand or machine wound coils; or if you use enamel, formvar or modem polyurethane coated wire, as long as the coil is perfectly wound and free of Short. It is true that enamel or formvar coated wires are not as delicate as modem, thin polyurethane coaled wires and are not as likely to cause internal shorts.

Internal Shorts are on the loose!

Recently, I've measured more than a hundred so-called Vintage Pickups, and there was the Bull! The amount of decay varied between five and fifty percent. Only a few of these pickup came close to the real thing.

Getting back to magnetism, a few percent loss of magnetism in a pickup is totally irrelevant, but is crucial in an ammeter where the magnetical circuit must be calibrated 3Ild stabilized for correct measuring results. As long. as a pickup is in a guitar and does not get in direct Contact with high coercive magnets or be exposed to temperatures below -120 degrees Fahrenheit or above +800 degrees Fahrenheit, there is very little chance that the magnets will lose some of their magnetism. If you degauss an Alnico magnet in a pickup, the magnet will lose its permeability causing a decrease of inductance in the coil and an increase in decay due to core loss."

Can anyone describe the nature of this "decay" and its measurement in terms this non-techie hobbyist might be able to understand?

Thanks in advance.

[big_teee]

That 4% is probably the settling in of magnets after a period of time, after charging.
It Seems that magnets stay charged better stuck to steel, or several magnets stuck together.
I've taken some A5 magnets out of old pickups that were still charged hot.
Ceramics seem to stay charged hot forever.
I used to use magnets less than fully gaussed, now I just use a weaker type magnet, at full gauss.
Like A2, or A3.
To me the degauss, or trying to charge less than full is a lot of trouble, and I always worry about will they stay charged.
T

[kayakerca]

That 4% is probably the settling in of magnets after a period of time, after charging.
It Seems that magnets stay charged better stuck to steel, or several magnets stuck together.
I've taken some A5 magnets out of old pickups that were still charged hot.
Ceramics seem to stay charged hot forever.
I used to use magnets less than fully gaussed, now I just use a weaker type magnet.
Like A2, or A3
T

I was thinking Bill Lawrence was on the minute shorts in the coil and I should have put more of the quote up. I am going to do that now. Sorry big_teee. I tried to do a smaller excerpt not to be so anal about things, but I now think more would have been better in this instance. I was focused on "Any additional decay is caused by minute shorts or even semi-shorts in the coil. These shorts are extremely hard to detect. However, in the past five years I have developed a measuring technique to detect these shorts." He actually may have only on about the magnets, but that would be easy to measure. I'm just not sure.

[big_teee]

I'm sorry I got on the wrong track.
I was thinking of gauss decay.
IMO no shorts are acceptable.
Especially on new SCs.
Most old Strat SCs have corrosion from the inside out.
Sweat and condensation that runs down the magnets.
That is why we tape, or dip.
T

[mcgruff]

A thousand turns, more or less, have very little effect on output or sound

don't know about that...

[kayakerca]

don't know about that...

Probably true, but what I'm really interested in understanding about is the decay caused by shorts and their measurement comment:

"additional decay is caused by minute shorts or even semi-shorts in the coil. These shorts are extremely hard to detect. However, in the past five years I have developed a measuring technique to detect these shorts"

[big_teee]

I would think with modern wires that shorts would be very minimal.
The only exception is the problem with magnet shorts on single coils.
The wire I've heard of that decays through time is PE.
Don't think varnish and Poly has the decay issues.
Mainly what Post CBS Fender used was PE.
The CBS pickups are usually the ones needing the repairs.
Maybe someone else has something to add here.
Any old pickups that come through here that have any issues get rewound.
Cheapest route I give is the Poly, If they want vintage type wire it is extra.
Most players just want them fixed the cheapest way.
T

[Joe Gwinn]

I have a 2 part question. I was reading a bunch of Bill Lawrence stuff today and was curious about the nature of the "decay" he referred to in the excerpt below from one of his articles and if it was something that was measurable by the hobbyist?

"I have measured the magnets of numerous and beautifully sweet sounding vintage strat pickups, and they have not lost any magnetism. The coils had up to ten percent tolerance in DC resistance caused by the tolerance of the coilwire and by the difference in tension at the coilwinder. This will have no influence on the sound of the pickup. One thing all these good sounding pickups have in common is they all have less than four percent decay. Three to four percent is the expected amount of decay due to core loss of fully magnetized Alnico V magnets. Any additional decay is caused by minute shorts or even semi-shorts in the coil. These shorts are extremely hard to detect. However, in the past five years I have developed a measuring technique to detect these shorts. If a coil is perfect, the pickup will sound great. A thousand turns, more or less, have very little effect on output or sound. There is no difference between layer or scatter wound, hand or machine wound coils; or if you use enamel, formvar or modem polyurethane coated wire, as long as the coil is perfectly wound and free of Short. It is true that enamel or formvar coated wires are not as delicate as modem, thin polyurethane coaled wires and are not as likely to cause internal shorts. ...

Can anyone describe the nature of this "decay" and its measurement in terms this non-techie hobbyist might be able to understand?

The issue is shorted turns in the coil. These shorts can be between the wire in various turns, or between wire and alnico magnets. The greater the fraction of the coil that's spanned by the short, the greater the effect on sound.

Typically, one cannot tell by measuring the DC resistance, but one can easily tell by measuring the AC resistance at 1000 Hz, using an Extech model 380193 handheld LCR meter. The added loss caused by the shorted turns shows up as increased AC resistance.

[kayakerca]

The issue is shorted turns in the coil. These shorts can be between the wire in various turns, or between wire and alnico magnets. The greater the fraction of the coil that's spanned by the short, the greater the effect on sound.

Typically, one cannot tell by measuring the DC resistance, but one can easily tell by measuring the AC resistance at 1000 Hz, using an Extech model 380193 handheld LCR meter. The added loss caused by the shorted turns shows up as increased AC resistance.

Thanks Joe.

Does that mean (in laymanish type terms), going back to the Bill Lawrence excerpt, the ratio would be something along the lines of:

(Rs - DCR) / DCR

Would a fair representation of the decay percentage due to minute shorts in the coil from in excess of "the expected amount of decay due to core loss of fully magnetized Alnico V magnets"?

. . . . . . .Addendum. . . . . . .

My laymanish thinking must be missing the boat on trying to understand how the measurement aspect of coil decal is would be calculated. I looked back at some of the measurements I take on my winds and even before I charge the Alnicos and pot, there is typically a 4% difference between the Rs and DCR. That difference increases by another 2% - 3% after charging Alnicos and potting. My minimal understanding of the physics of it all is a frustrating thing at times.

[Joe Gwinn]

Thanks Joe.

Does that mean (in laymanish type terms), going back to the Bill Lawrence excerpt, the ratio would be something along the lines of:

(Rs - DCR) / DCR

Would a fair representation of the decay percentage due to minute shorts in the coil from in excess of "the expected amount of decay due to core loss of fully magnetized Alnico V magnets"?

It isn't clear to me what Bill meant. Perhaps he expands on the issue elsewhere than the quote.

. . . . . . .Addendum. . . . . . .

My laymanish thinking must be missing the boat on trying to understand how the measurement aspect of coil decay would be calculated. I looked back at some of the measurements I take on my winds and even before I charge the Alnicos and pot, there is typically a 4% difference between the Rs and DCR. That difference increases by another 2% - 3% after charging Alnicos and potting. My minimal understanding of the physics of it all is a frustrating thing at times.

The difference between the LCR Rac measurement (in SER (series) mode) and the multimeter Rdc measurement is due to eddy current loading. Search the forum for for my many discussions of eddy currents. This is much discussed.

[big_teee]

So what is the point of this measuring. Let's put this in a practical application?
If you have a certain percent of shorted coils on new pickups, do you rewind them?
This sounds like if your having this issue on new pickups, It would be with the tensioning device of an auto winder.
Wire scuffing?
T

[kayakerca]

So what is the point of this measuring. Let's put this in a practical application?
If you have a certain percent of shorted coils on new pickups, do you rewind them?
This sounds like if your having this issue on new pickups, It would be with the tensioning device of an auto winder.
Wire scuffing?
T

I do not put every set of pickups I wind into a guitar and test them prior to handing them over to a customer. Maybe you and everyone else here does, but I don't. I wind a to certain number of turns at a predetermined tpl and tension and I compare the resultant DCR and Inductance to the target values for the particular pickup I am winding. If they are within a variance level I am good with, in the package they go.

If there is something wrong with the wind that wouldn't show up in the DCR and inductance reading and I am able to measure it, I want to, so I can pull the puppy apart and start over. That is the practical application.

So to some numbers. Below is a set of the readings (from a sample wind) I take in addition to the DCR for every wind. If one or more of those values (or a calculation based on the interrelationship of those values) indicates something is out of whack while the DCR and Inductance looks in line, I think it would be of value to know so, as I was saying, I can tear it apart and start over. In fact, I know it would be of value. This somehow did not seem like an unreasonable approach to my way of thinking.

Pickup Spec Comparisons 2013 01 10a.pdf

[big_teee]

I don't test all pickups either, just for certain price ranges for certain customers.
Only if I have time, if I feel like experimenting, and if I did something a little differrent, and want to know what they sound like.
I was just trying to tie the OP to what the practical application is, and you did that here.
So I guess unless you have a large variation, then in the package they go.
So if you have one that doesn't pass the smell test, then have you been able to isolate the cause.
That would be what I would want to know, What the cause of the defect is.
T

[kayakerca]

. . . I guess unless you have a large variation, then in the package they go.
So if you have one that doesn't pass the smell test, then have you been able to isolate the cause.
That would be what I would want to know, What the cause of the defect is.
T

I agree, if I had a defective coil, I'd want to try and figure out what was defective and what caused it. But to this point (which for me is only a very short distance from the starting blocks) I haven't had a wind that didn't measure within what I take as reasonable tolerance limits. I'm thinking it would be hard to figure out the cause of a defect in many cases by actually being able to physically see it. From measurements, for sure, but seeing it I'm guessing would be a challenge in a lot of situations (e.g. shorts in a coil that was not broken).

Have you had defects you were able to visibly detect after you found the defect by some measurement parameter?

[big_teee]

I had a single coil go short to the magnets after potting once.
That was before I got more concerned about taping the magnets.
It worked fine, but I tore it down and rewound it anyway.
I had a 50s HFV rewind once that visibly looked fine.
I peeled some of the wire off and counted turns, and couldn't find anything wrong.
I hammered out the magnets on one end and slipped the coil off the magnets.
It was eat up inside where the coil was resting against the magnets.
I gave the coil to the owner, so he would believe I rewound it.
That one had no visible sign of varnish dipping.
It came out of a night club guitar. Sweat and beer running down the coil I suppose?
I taped the magnets and went back with vintage HFV wire.
Modern day wax potting pickups should also help some on insulation and stability.
It would be hard for the wire to decay much encased in a thin layer of wax?
The old gibson coils used the same wire, but were more stable.
wound on a butyrate plastic bobbin, then taped, then covered with a nickel cover.
Some go bad, but they have a much better track record than the CBS fender Pickups.
I wonder if Seymour Duncan had much to say about this in his notes?
T