Inductance Puzzle

[Jason Robitaille]

Hi guys, I've been winding Telecaster Bridge pickups recently and I wound one with Alnico2 magnets and 9200 winds of #42 and approximately like 15g of tension.. It didn't sound amazing to me, maybe a touch too much high frequencies compared to a USA tele, but I checked the Inductance on it and it came in at a surprising 3.8H.. the DC reading was like 7.2k... So I decided to wind another the exact same way and the 2nd time the inductance was 3.1H? and the DC reading was 7.1k.. This was like a huge discrepancy in my mind.. So i decided to wind a 3rd one except this time i decided to scatter like crazy to make the coil as big as possible to see how it would affect the inductance and the last one came in at 3.3H!?

Basically what i'm wondering is how the heck did I manage to get 3.8H the first time! I've always wound the same kind of way. I don't have a very high TPL, maybe 50 - 60. Does doing the opposite (mechanical and high TPL) make the inductance go up?

I'll continue doing tests, but I just wanted to know if anyone could hint me in the right direction on what controls Inductance other than magnet strength.

I also tend to keep my coils slightly rounded across the length of the poles so that the top and bottoms come in a little.

all pickups only have 9200 winds and they all are around 7.2k.

any help is greatly appreciated.

[big_teee]

I didn't see where you measured the magnet gauss?
T

[Jason Robitaille]

Hey Big_Tee, all the magnets are measuring approximately 450 Gauss.. I'll double check again tonight, but I think they are all in the same zone which is why i'm so confused, I thought maybe the first pickup had alnico 5, but okay thanks for the tip.

-Jason

[Jason Robitaille]

Assuming all things are equal, # of winds, magnet strength and tension, would there be anything regarding the wind pattern which would explain a 0.5Henry difference? it feels like a lot.

[big_teee]

Not sure, I don't have anyway to measure for inductance.
Some of the others here, may be able to answer what range the inductance should be.
If all things are equal, they should be similar.
What they sound like is what is important to me.
T

[mozz]

Higher gauss has nothing to do with higher inductance. Actually lower gauss, A2 magnets, have more iron, hence higher inductance. If you wind very neatly, like each wire parallel touching the next, like a machine wound pickup, you will get higher inductance. So, even if you wound 3 pickups with exactly the same number of turns, your inductance will change every time, unless you are a machine.

[big_teee]

Higher gauss has nothing to do with higher inductance. Actually lower gauss, A2 magnets, have more iron, hence higher inductance. If you wind very neatly, like each wire parallel touching the next, like a machine wound pickup, you will get higher inductance. So, even if you wound 3 pickups with exactly the same number of turns, your inductance will change every time, unless you are a machine.

Mozz that makes sense.

This is just a basic winding forum, and we usually leave the measuring, and theory to the regular forum.
If need be I can move this over there.
Here we are more into wind what sounds good, basic winding methods, & techniques.
I finally graduated to a winder with a counter, and a gauss meter!
What the inductance is, to me, is of no concern if the pickup sounds good.
GL,
T

[Lollar Jason]

Higher gauss has nothing to do with higher inductance. Actually lower gauss, A2 magnets, have more iron, hence higher inductance.
well al 2 will give you higher inductance than 5 but a discharged five will give less inductance than a fully charged five etc. Shorter coils will give higher inductance than taller coils and as mozz stated more tpl will give higher inductance as will a steel reflector plate. In some cases a well fit steel coupling will increase inductance over a poor fitting steel coupler- not completely sure about tele bottom plates but it makes a big difference on something like a rhodes pickup- how well the metal tip contacts the magnet.

[mozz]

I stand corrected on the higher does not =higher. Why was i thinking the gauss had no effect on inductance? I fully dis-charge when building then fully charge when done, then calculate resonant freq. I've only wound about 20 sets, so still learning, but into electronics and tubes for 40 years. I first noticed a strat set with A5 had 2.2 henries or so, when i wound a set with A2 or A3 the inductance readings were higher, then i read up on different formulas for magnets and figured the more iron made it a better inductor. So now i have more work to memorize. Higher H or pf= lower resonant freq, Lower H or pf = higher resonant freq.

"Why was i thinking the gauss had no effect on inductance?" I know why i was thinking that way, working with rf electronics it is usually ferrite cores of varying types or air cores. As far as i know, ferrite won't take a "static" magnetic charge. So i must have put it in my head that a "static" magnetic charge will not effect the permeability of a coil, i'm totally lost now. All i know is in RF, you would not want the fixed inductance to permanently change and need to rely on the properties of the core material. Maybe it's all the same.

[Jason Robitaille]

Wow Jason thank you soo much, I just got my vernier calipers out and it looks like my original pickup is slightly shorter than the rest.... UGHHHH!!! I've really got to make sure i'm more consistent with my installation jig, everything is making sense now. I think I've got to take my Tele Bridge bobbins down in height because when I compare it against a USA tele my bridge is ALWAYS brighter in the very highest end frequencies. even when i feel like i'm overwinding (i've tried like 10,000 winds of #42) my bobbins between the flats are measuring 0.478 which i took from a MiM ceramic bridge.

-Jason