Bobbin dimensions/windings

[Stratz]

Math has never been my strong suit.
Can any of you members please tell me how to calculate the difference or ratio in the number of winding's for the following.

Say I have a 50mm HB bobbin with 5,000 winds and it reads 3.7k.
How can I calculate the number of winding's to yield the same DC resistance on 49.2mm and 53mm bobbins.

Thanks.

[David King]

This may seem like an odd question but why are you wanting to match the DCRs?

[Stratz]

Because I need something to base the windings on. I could use inductance if that helps.
I have some recipes that were originally done with 50mm HB bobbins. I'd like to transfer them to 49.2mm bobbins and see how they sound.

[copperheadroads]

I've only noticed a slight increase in DCR when winding on a 50mm bobbin compared to a 49.2mm bobbin so I really never worry enough to adjust it but if you want to 50 turns per bobbin always worked for me or add 1%
as for 53mm compared to 50 you want to roughly deduct 4.5% of winds ..

[Stratz]

I've only noticed a slight increase in DCR when winding on a 50mm bobbin compared to a 49.2mm bobbin so I really never worry enough to adjust it but if you want to 50 turns per bobbin always worked for me or add 1%
as for 53mm compared to 50 you want to roughly deduct 4.5% of winds ..

Thank you sir.

[jack briggs]

I agree with the others - number of turns is what I'd use.
BTW - it would be more a matter of geometry + math. You'd want to have actual bobbins in hand to get ID measurements, but I'd see it as kind of a moot point....

cheers,

[salvarsan]

Starting from a 50mm bobbin, 5000 winds 42AWG is 3715 ohms.
The internal core length changes -0.8 and +3.0 mm for 49.2 and 53 mm bobbins.

Adjusting the core length in inches on the Coil Estimator you get

• 50.0 mm -- 5015 winds
• 49.2 mm -- 5070 winds = +55
• 53.0 mm -- 4825 winds = -185

You may not hear difference from an additional 55 winds but 185 fewer should be audible.

[edit]

The Coil Estimator web app has been updated to include some 49.2 and 53 mm PAF bobbins in its list.
Those derive from actual measurements and show that the core length changes according to manufacturor rather than the pole spacing.

core length (inches)	source
2.225	PAF 50mm generic
2.218	PAF 49.2mm Gibson Burstbucker2
2.200	PAF 49.2mm Mojo
2.203	PAF 49.2mm Mojo/WSC
2.250	PAF 49.2mm Stew-Mac
2.330	PAF 53mm Guitar Jones Cream Slug
2.317	PAF 53mm Mojo

-drh

[Stratz]

The Coil Estimator web app has been updated to include some 49.2 and 53 mm PAF bobbins in its list.
Those derive from actual measurements and show that the core length changes according to manufacturor rather than the pole spacing.

Thanks very much

[salvarsan]

You'd want to have actual bobbins in hand to get ID measurements, . . .

After seeing how the bobbin sizes are so variable, I agree.

An inexpensive 6" dial caliper seems like $20 well spent. I get tired of seeing low batteries on my digital ones.

-drh

[LtKojak]

Starting from a 50mm bobbin, 5000 winds 42AWG is 3715 ohms.
The internal core length changes -0.8 and +3.0 mm for 49.2 and 53 mm bobbins.

Adjusting the core length in inches on the Coil Estimator you get

• 50.0 mm -- 5015 winds
• 49.2 mm -- 5070 winds = +55
• 53.0 mm -- 4825 winds = -185

You may not hear difference from an additional 55 winds but 185 fewer should be audible.

[edit]

The Coil Estimator web app has been updated to include some 49.2 and 53 mm PAF bobbins in its list.
Those derive from actual measurements and show that the core length changes according to manufacturor rather than the pole spacing.

core length (inches)	source
2.225	PAF 50mm generic
2.218	PAF 49.2mm Gibson Burstbucker2
2.200	PAF 49.2mm Mojo
2.203	PAF 49.2mm Mojo/WSC
2.250	PAF 49.2mm Stew-Mac
2.330	PAF 53mm Guitar Jones Cream Slug
2.317	PAF 53mm Mojo

-drh

This is one of the most useful, yet overlooked measures to account for when winding p'ups: the actual bobbin's shape and dimensions. This factor will most likely affect the most the outcome of your winding, the same amount of turns, TPL and tension could generate a bigger or smaller bobbin, actually affecting the distributed capacitance, ultimately dulling or sharpening the tone.

I knew they were differences among manufacturers, but seeing that the Stew-Mac 49.2mm bobbin's core is even bigger than the generic 50mm is kinda a wake-up call to me.

Thank you Stratz and Salvarsan.

[big_teee]

Starting from a 50mm bobbin, 5000 winds 42AWG is 3715 ohms.
The internal core length changes -0.8 and +3.0 mm for 49.2 and 53 mm bobbins.

Adjusting the core length in inches on the Coil Estimator you get

• 50.0 mm -- 5015 winds
• 49.2 mm -- 5070 winds = +55
• 53.0 mm -- 4825 winds = -185

You may not hear difference from an additional 55 winds but 185 fewer should be audible.

[edit]

The Coil Estimator web app has been updated to include some 49.2 and 53 mm PAF bobbins in its list.
Those derive from actual measurements and show that the core length changes according to manufacturor rather than the pole spacing.

core length (inches)	source
2.225	PAF 50mm generic
2.218	PAF 49.2mm Gibson Burstbucker2
2.200	PAF 49.2mm Mojo
2.203	PAF 49.2mm Mojo/WSC
2.250	PAF 49.2mm Stew-Mac
2.330	PAF 53mm Guitar Jones Cream Slug
2.317	PAF 53mm Mojo

-drh

IME unless you have some older nom/max large low resistance wire, you may not be able to achieve these turn specs.
Wire these days is running on the very smaller side.
typical 42 single is .0026-.00268", and running over 1700 ohms per 1000 feet of wire.
Just wanted to make all aware of the wire size discrepancies.
43, and 44 is also smaller respectively.
T