Bicentennial Firebird Pickup -- Magnet

[Zhangliqun]

I guess my real question then is about wiring the coils in series and how they should be oriented toward the pickup. We're assuming both are wound the same -- just as in a standard humbucker. But either you wire them standard (start leads soldered together or finish leads soldered together) or it's Coil A finish to Coil B start or vice versa.

Bobbin orientation -- yes, I know, 90 degrees or sitting sideways, hence the name. But is it both with bobbin "bottom" (where leads come out) facing/touching the magnet or both "top" facing/touching the magnet? Or Coil A bottom facing magnet and Coil B top facing magnet on the other side?

This "null" positioning on the magnet really raises a lot of questions, at least for me.

[big_teee]

Put the magnet edge North up.
Wind both mini coils just like big PAF humbucker coils.
Mark the top of the bobbins.
Put both bobbins tops against the bar magnet.
Now wire + output to first coil start lead.
Wire the Finish lead of the first coil to the start lead of the second coil.
Wire the finish of the second coil to ground.
T

[rjb]

Since T answered the first half of your question (post #16), I'll take a shot at the second half.

This "null" positioning on the magnet really raises a lot of questions, at least for me.

First, disavow yourself of any notion you may have that pickups produce a voltage when "the string disturbs the magnetic field".
Instead, accept the model that says the magnet magnetizes a part of the string- and when the string vibrates, that moving magnet induces a voltage in the coil.
So, the shape of the permanent magnetic field doesn't matter much, as long as it magnetizes the string.
With the magnet in "null" position, the top magnetizes the string, and the bottom is too far away to do much of anything.
Sure, that's vague hand-waving- but no more than "for reasons not known, this works fantastically well".

I'm trying to think of a good way to explain why the voltages induced in the two coils add together, but it's way past my bedtime.

[Alberto]

Since T answered the first half of your question (post #16), I'll take a shot at the second half.


First, disavow yourself of any notion you may have that pickups produce a voltage when "the string disturbs the magnetic field".
Instead, accept the model that says the magnet magnetizes a part of the string- and when the string vibrates, that moving magnet induces a voltage in the coil.
So, the shape of the permanent magnetic field doesn't matter much, as long as it magnetizes the string.
With the magnet in "null" position, the top magnetizes the string, and the bottom is too far away to do much of anything.
Sure, that's vague hand-waving- but no more than "for reasons not known, this works fantastically well".

I'm trying to think of a good way to explain why the voltages induced in the two coils add together, but it's way past my bedtime.

So, an Alnico8 magnet and two bobbins without any steel inside should work as well...

[rjb]

So, an Alnico8 magnet and two bobbins without any steel inside should work as well...

No, I didn't mean to imply that.
The steel "steers" the flux through the coils.
But an Alnico magnet and two bobbins with steel inside would be more efficient than a ceramic magnet and two bobbins with steel inside.
I really do need to go to bed now.

[David King]

Late to the party here... Most if not all of the sidewinder's I've seen had the magnets inside the coils and the steel plate or poles pointing at the strings coming up through the middle. I can see how this version might work; the magnet magnetizes the strings and the iron cores draw the flux through the coils but I'd think having two additional magnets on the outsides of the coils would help complete the circuit and boost efficiency. I'm willing to bet that the magnet in the photo above doesn't go all the way to the bottom but stops 1/2 way down. Having the coil cores come in at the neutral point of the magnet makes no sense to me either but maybe it works just fine though it's also possible that the baseplate is steel and helps complete the magnetic circuit up the outsides.

[big_teee]

No steel in the pickup that I can see.
See pictures.
Vintage Firebird Pickups | Bicentennial | Medallion

There is no room for additional magnets, and yes the magnet is the width of the bobbin flange.
See Patent.
Patent US3902394 - Electrical pickup for a stringed musical instrument - Google Patents
T

[David King]

Thanks Terry,

I've never looked into these before and a fact-based reality check is what I needed. Thanks! Back to my armchair...

[rjb]

Oops, I think we may have made a boo-boo.

I just bumbled upon a pertinent old thread, then went back and re-read "the article" more carefully.

In this article, the author merely speculates that this patent (filed by Bill Lawrence, Aug. 1974) was used for the bridge pickups in the 1976 Bicentennial Firebird guitars and Thunderbird basses.

My guess is that he designed the pickup at an earlier point, and although he wasn't working for Gibson at the time had applied for the patent there because Gibson wanted to begin using them at that point for the Bicentennial Firebirds as well as the Thunderbirds.

In this post, David Schwab details the construction of a 1976 Bicentennial Thunderbird pickup. The attached photo of said dissected pickup shows a 1/16" thick steel blade running through both coils; a gap between the bobbins shows where an alnico magnet once sat atop the blade.

I still haven't found a confirmed gut shot of a Bicentennial Firebird pickup- but if it uses the same design as the Bicentennial Thunderbird pickup, it does not employ the "null magnet" configuration detailed in patent US3902394.



Snarky comment:
The author of that article clearly suffers from both verbal diarrhea and clinical naivete.

Bill passed away in Nov. 2013 but his legacy is being carried on by another gentleman who worked with Bill for a long time and who now runs Bill Lawrence USA.

[big_teee]

The picture that david shows of the 76 tbird is not the same pickup in the 76 firebird article.
You will notice that the bobbins are much taller between the flats in the firebird article.
Those bobbins are the regular mini bucker bobbins.
The picture of the t-bird pickup also doesn't match the patent.
The pickups in the firebird article do, if the magnet goes all the way through.
It all seems to be smoke, mirrors and mythological.
They had the pickups a part, why didn't they take pictures from all angles?
It must have not been that great of a pickup, if it only lasted 3 years or so!
T

[rjb]

We do know that the picture David shows is of an actual 1976 Bicentennial Thunderbird pickup.
How do we know? Because it was David's pickup, and he seems to keep pretty good records of such things.

We do not know that the photo in the article is of an actual 1976 Bicentennial Firebird pickup.
Why not? Because the author himself does not know. Here's what he said:

Here is a photo of one, perhaps from a Bicentennial Firebird, not quite sure. But you can see it is very very similar to the dissected 82 pup from the beginning of this page.

Sidewinder pickup from a Thunderbird, not sure of the exact year.

We do not know that the patent had anything to do with the 1976 Bicentennials.
Why not? Because it was just a wild-assed guess by the author.

My guess is that he designed the pickup at an earlier point, and although he wasn't working for Gibson at the time had applied for the patent there because Gibson wanted to begin using them at that point for the Bicentennial Firebirds as well as the Thunderbirds.

It is not clear to me that the author had any of his own pickups apart.
It appears he was brave enough only to examine the backs of his pickups, and included "found" gut shots for reference.

It doesn't matter if the 1976 Bicentennial Firebird pickup is a great pickup. It's what the customer wants.

Now some speculation of my own:
It would make marketing sense for "special edition Bicentennial commemorative" guitars to sport "unique" features- such as "newly designed pickups that look forward to the next 200 years" or some-such. (Can you tell I'm not a marketing guy?)
It would also make sense for matching-pair Bicentennial Firebird guitars and Thunderbird basses to sport matching pickup designs.
Ergo, it makes sense that the 1976 Bicentennial Firebird pickup would look a lot like David's 1976 Bicentennial Thunderbird pickup.

-rb

[big_teee]

OK, I guess it's David's pickup.
Where is the magnet for the pickup?
I see two bobbins, and a blade.
I don't see a magnet?
So far on this 76 bicentennial quest, I haven't seen a whole anything.
Without knowing what you are building, it is hard to duplicate it!
Too much hype here for me.
I'll stick with a magnet in each bobbin and a thin blade in the middle.
The statement made that the steel blade thickness doesn't matter?
I've found that IME, all quanities of steel matters!
The more steel the darker the tone.
T

[rjb]

Yes, without knowing what you are building, it is hard to duplicate!
But I think we're a little closer to knowing what to duplicate.
David said the pickup used an alnico magnet.
Although the magnet isn't shown in the photo, you can clearly see its footprint.
So we know its length and thickness, but we don't know its width (how far it sticks up above the top).
But I would guess that the magnet Mojotone lists as "for Firebird pickups" is close enough.
Alnico 5 Cast Bar Magnet 2.050'' Long

Too much hype? It's all about the hype.
Gear that didn't sell well when new (because it sucked) becomes valuable collectible (because its rare).
Old gear that young musician bought because it was cheap becomes priceless when musician becomes a rock star.

If you don't buy into the hype (or have customers who do), you can do whatever you want.

David didn't say steel blade thickness "doesn't matter". He said he has wound bright (bass) pickups with thick blade cores and bright sidewinders with an 1/8" steel core, concluding "I think it's safe to say the affect of the core on the high frequencies in these pickups is less than expected." Whatever works, works.

-rb

[big_teee]

You may be closer, I'm not.
Still keep in mind that the pickup had a 3 year shelf life.
It appears it would be a very inefficient pickup design.
Most sidewinders are weak and anemic.
It takes lots of magnetism to make them loud enough.
That was the reason for the mudbucker having those enormous coils, and four magnets.
I agee that was overkill, but a means to an end.
The internal magnet design I use, overcomes anemia with 2 large internal 1500 gauss ceramics, head to head against a thin blade.
One in each coil.
Gibson, shortly went back to the rock solid magnet in a coil humbucker design, and the rest is history!
Anyway the OP, has moved on.
Nothing here in this thread, I would waste labor and parts on.
But, YMMV!
T

[rjb]

OK, I'm done too.

Later, Everybody.
-rb