New Mojotone Butyrate humbucker bobbins. How accurate are they ?

[Fuzzy Logic]

An attempt to recreate the main dimensions of a vintage P.A.F. humbucker - Part 6 - A P.A.F. humbucker slug bobbin and P90 bobbin connection ?

The presumed main dimensions for a P.A.F. humbucker slug and screw bobbin as described in parts 1-5 were finalized by me about a month ago. Last week I stumbled across some topics which contained a number of dimensions for P90 bobbins.

Now, I never really checked out the P90 bobbin although I was aware of the fact that the P.A.F. humbucker was intended to be a hum free version/replacement of/for the P90 pickup.

These are the topics I am referring to:

P90 construction , source: Jonson

Bobbin length: 3.00" , bobbin width: 1.118" , bobbin height: 0.375" , core height: 0.235". The core height of 0.235" appears to be a bit questionable and was not measured inside the bobbin at the core itself. In that same topic it is also mentioned that the core dimensions were supposed to be 0.250" (height) and 0.250" (width).

Bobbin Support , source: Possum

In this topic the core dimensions are stated as being 0.250" (height), 0.250" (width) and 2.50" (length).

Otherwise, there is very little information available about the dimensions for P90 bobbins. Sometimes there is a reference to a drawing by Jason Lollar but I am not sure if this drawing depicts a "vintage correct" P90 bobbin.

The bobbin width of 1.118" appears to be a little off spec. All other dimensions can be perfectly expressed as multiples of (1/8)", (1/16)", etc. This 1.118" value doesn't express itself very well that way and this is a little bit suspicious. So, we divide 1.118" by (1/8)". The result of 8.944 is very close to a factor 9. This suggests an intended bobbin width of 1.125".

P90 bobbin length : 3.000"
P90 bobbin width : 1.125"
P90 bobbin height : 0.375"
P90 core length : 2.500"
P90 core width : 0.250"
P90 core height : 0.250"
P90 maximum winding depth (along the width of the bobbin): (3.000" - 2.500")/2 = 0.250"
P90 maximum winding depth (along the length of the bobbin): (1.125" - 0.250")/2 = 0.4375"

P.A.F. slug bobbin length : 2.6250"
P.A.F. slug bobbin width : 0.6875"
P.A.F. slug bobbin height : 0.3750"
P.A.F. slug core length : 2.1875"
P.A.F. slug core width : 0.2500"
P.A.F. slug core height : 0.2500"
Maximum winding depth slug bobbin (along the width of the bobbin): 0.21875"
Maximum winding depth slug bobbin (along the length of the bobbin): 0.21875"

Now, let's see if there is some kind of correlation between the dimensions as listed above. I am now going to normalize the P90 bobbin dimensions by dividing the dimensional values by themselves. Then I divide the dimensions of the P.A.F. humbucker bobbin by the values of the corresponding dimensions of the P90 bobbin.

P90 bobbin length : 1
P90 bobbin width : 1
P90 bobbin height : 1
P90 core length : 1
P90 core width : 1
P90 core height : 1
P90 maximum winding depth (along the width of the bobbin): 1
P90 maximum winding depth (along the length of the bobbin): 1

P.A.F. slug bobbin length : 0.875
P.A.F. slug bobbin width : 0.611
P.A.F. slug bobbin height : 1
P.A.F. slug core length : 0.875
P.A.F. slug core width : 1
P.A.F. slug core height : 1
Maximum winding depth slug bobbin (along the width of the bobbin): 0.875
Maximum winding depth slug bobbin (along the length of the bobbin): 0.5

Well, the 0.611 appears to be off at first sight but this is because the P90 bobbin is asymmetrical when looking at winding depth as opposed to the P.A.F. humbucker bobbin which is symmetrical for winding depth. This scaling factor of 0.611 is effectively causing a conversion from a asymmetrical winding depth to a symmetrical winding depth.

Given the scaling factors as derived above, this appears (!) to be proof that the P.A.F. humbucker slug bobbin was derived directly from a P90 bobbin.


Next: Part 7 - What about that core height increase for a P.A.F. humbucker bobbin ? (last part).

[Fuzzy Logic]

An attempt to recreate the main dimensions of a vintage P.A.F. humbucker - Part 7A - What about that core height increase for a P.A.F. humbucker bobbin ?


As I pointed out in part 1 of this saga, WolfeMacleod has indicated in this thread that the core height of a P.A.F. humbucker bobbin is supposed to be larger than 0.250", about 0.015" larger as he stated. I also pointed out in part 1 that I suspected that the height increase is probably something like (1/64)", resulting in a core height of 0.265625".

I did not use this core height of 0.265625" in my explorations as documented in parts 1-7 and for good reason. I first wanted to attempt to establish some kind of a timeline, assuming that the P.A.F. humbucker bobbins may have been revised during the lifecycle of the P.A.F. humbucker. Although parts 1-6, and this part, could equally be perceived as being fiction, non-fiction or even science fiction, there appears to be compelling evidence that a P.A.F. humbucker slug bobbin having a core height of 0.250" is a descendant of a P90 bobbin. So the order of appearance would be: P90 bobbin -> P.A.F. humbucker bobbin with 0.250" core height (revision 0).

So, what could be a reason to change the core height from 0.250" to 0.265625" ? (please note: I am aware that stating a dimension of 0.265625" is a bit meaningless since it it obvious that it is not possible to manufacture a plastic part with such accuracy).

In order to formulate some kind of plausible explanation we need to go back a bit to the P90 bobbin. Usually it is stated that the P90 pickup is created by winding 10000 turns of AWG 42 onto the bobbin. Let's explore this for a while and turn ourselves into design mode. Winding 10000 turns of AWG 42 (min-nom) with a TPL of 68 (actually an alternating TPL of 68/67) will yield the following values across the min-nom range for the magnet wire diameter:

Wire diameter: 0.0025" bare wire diameter + 0.0002" insulation
Number of turns: 10000
Winding depth: 0.2000"
Winding clearance to edge of flange: 0.0500"
DCR: 8176 Ohms
Inductance: 6.7H (approximate value)

Wire diameter: 0.0024" bare wire diameter + 0.0002" insulation
Number of turns: 10000
Winding depth: 0.1926"
Winding clearance to edge of flange: 0.0574"
DCR: 8840 Ohms
Inductance: 6.8H (approximate value)

When taking the min-nom tolerance of the magnet wire into account, the DCR value of a P90 pickup would always fall within the range of 8.2 - 8.8 kOhms. It is assumed that the range of DCR values will manifest itself in a gaussian distribution.

Now, let's take this design into production for prototyping and actually wind a few pickups. We check the prototypes for DCR values and we find that the range of DCR values is actually ranging from 8.5 kOhms to 9.2 kOhms. To make a long story short; during the winding process the magnet wire has been stretched and the magnet wire on the bobbin now has a reduced diameter causing the DCR value of the magnet wire to go up and this results in DCR values of the prototype pickups which is higher than it was designed to be.

Wire diameter: 0.00245" bare wire diameter + 0.0002" insulation
Number of turns: 10000
Winding depth: 0.1963"
Winding clearance to edge of flange: 0.0537"
DCR: 8496 Ohms
Inductance: 6.7H (approximate value)

Wire diameter: 0.0024" bare wire diameter + 0.0002" insulation
Number of turns: 10000
Winding depth: 0.1926"
Winding clearance to edge of flange: 0.0574"
DCR: 8840 Ohms
Inductance: 6.8H (approximate value)

Wire diameter: 0.00235" bare wire diameter + 0.0002" insulation
Number of turns: 10000
Winding depth: 0.1889"
Winding clearance to edge of flange: 0.0611"
DCR: 9203 Ohms
Inductance: 6.8H (approximate value)

There are two things one could do at such a moment. One can choose to leave it like it is or one can choose to adjust the design so that the results in production (DCR value of the pickup in this case) will match the results as the designer(s) originally intended them to be. It appears that the designer(s) at Gibson went for option number 2 and decided to reduce the number of windings to 9600 when winding a P90 pickup with AWG 42 magnet wire having a nominal bare wire diameter of 0.0025".

Wire diameter: 0.00245" bare wire diameter + 0.0002" insulation
Number of turns: 9600
Winding depth: 0.1884"
Winding clearance to edge of flange: 0.0616"
DCR: 8122 Ohms
Inductance: 6.3H (approximate value)

Wire diameter: 0.0024" bare wire diameter + 0.0002" insulation
Number of turns: 9600
Winding depth: 0.1849"
Winding clearance to edge of flange: 0.0651"
DCR: 8452 Ohms
Inductance: 6.3H (approximate value)

Wire diameter: 0.00235" bare wire diameter + 0.0002" insulation
Number of turns: 9600
Winding depth: 0.1813"
Winding clearance to edge of flange: 0.0687"
DCR: 8798 Ohms
Inductance: 6.3H (approximate value)

The DCR values of the production samples of a P90 pickup would now fall into the range of 8.1 - 8.8 kOhms and will have an average DCR value of 8.5 kOhms.

It looks like this exercise yields at least plausible values for DCR. The average DCR value of 8.5 kOhms corresponds with statements made by respectable manufacturers. One example is here (see the text next to the pictures in the article):

Ref: P-90 Primer - Premier Guitar


Next: Part 7B - What about that core height increase for a P.A.F. humbucker bobbin ?

[WolfeMacleod]

Jeebus, you're putting a lot of work into this.

[big_teee]

Jeebus, you're putting a lot of work into this.

I agree, Why?
Buy a humbucker Kit!
T

[big_teee]

I see your alias serves you well.

Your Earlier Question???
The Answer is, Part of the Problem!
B_T

[copperheadroads]

I will read all of this thread one day

[Fuzzy Logic]

Your Earlier Question???
The Answer is, Part of the Problem!
B_T

Thank you. However, a more constructive approach would be to point out any flaws in my work as to substantiate your opinion. The level of detail I have chosen was intentional and designed to make that as easy as possible.

[Fuzzy Logic]

I will read this all of this thread one day

Thank you. Please report back at your convenience in case you find any flaws in my work.

[Fuzzy Logic]

Jeebus, you're putting a lot of work into this.

Well, I guess that you and the other manufacturers/winders here have spent way much more time at researching this subject than I have done up to now, which implies that it is very well possible that I went seriously off track somewhere in my posts.

[Fuzzy Logic]

I agree, Why?
Buy a humbucker Kit!
T

I think you may misunderstand the nature of my posts.

The title of this topic is "New Mojotone Butyrate humbucker bobbins. How accurate are they ?" Apparently, from reading the initial posts, nobody appears to be willing or able to (fully) answer this question (in public). So answering this question is what I attempt to do at the best of my ability. And if the general consensus is that what I have written up to now should be dismissed as being wild speculation only or simply a waste of time, so be it. But I hope that you can at least appreciate the effort of what I am trying to do here.

[David Schwab]

I think you may misunderstand the nature of my posts.

The title of this topic is "New Mojotone Butyrate humbucker bobbins. How accurate are they ?" Apparently, from reading the initial posts, nobody appears to be willing or able to (fully) answer this question (in public). So answering this question is what I attempt to do at the best of my ability. And if the general consensus is that what I have written up to now should be dismissed as being wild speculation only or simply a waste of time, so be it. But I hope that you can at least appreciate the effort of what I am trying to do here.

I think you certainly provided a wealth of info on the difference in geometry of the various bobbins. And that should answer the original question.

I guess people were looking for an easy answer of yes or no.

[RedHouse]

...you may misunderstand the nature of my posts...

Let's not get off-track now Fuzzy, you're almost done, keep the focus (part 7b?).

[Fuzzy Logic]

Let's not get off-track now Fuzzy, you're almost done, keep the focus (part 7b?).

Sure, I intend to finish what I started. Part 7B will be an attempt to identify the (most) probable reason why the core/bobbin height was increased. After that there will also be a part 7C which will be an attempt to explain why this small increase in height caused a apparent large effect on the consistency of the produced P.A.F. humbuckers.

[the great waldo]

Blimey

All I wanted to know was if the bobbins moulded from an original paf bobbin, or at least the dimensions the same. Due to cellulose laquer spraying pearl dust and possibly altzheimers supported by hefty applications of Guiness Lager and curry and thirty years in the buissness, I have forgotten what the old ones I took apart in the 70´s looked like. I had the impression that they had the mouldings inside like the normal non cab bobbins from mojo and some later Gibson pups that I saw. It would be nice If one of the forum members could post a photo of a bobbin or pair of bobbins. It´s all getting a bit technical.

Cheers

Andrew

Sure, I intend to finish what I started. Part 7B will be an attempt to identify the (most) probable reason why the core/bobbin height was increased. After that there will also be a part 7C which will be an attempt to explain why this small increase in height caused a apparent large effect on the consistency of the produced P.A.F. humbuckers.

[David Schwab]

Part 7B will be an attempt to identify the (most) probable reason why the core/bobbin height was increased.

Maybe so people can wind hotter pickups?