Greco Thunderbird II on Ebag

[ThunderBucker]

Hi Baz, looks like I dropped the ball on that one, sorry, but you *do* have my email and phone number, you could have given me a kick in the butt to remind me.  I do have the pickup, is this the one?  If so, I'll get to it later this week.  OK to post at this forum?

[Highlander]

... OK to post at this forum?

Far too polite for us...

[TBird1958]

Hey, there's that poor little lamb that lost it's way 

[Bionic-Joe]

Oh yeah, All good, I know...I should have called...Just was reminded of it. Any possibilities? The tone of these is sick??? Can it be duped???

[Bionic-Joe]

The split coil is similar to a Fender Precision split pickup...  Great Tone!!!

[godofthunder]

Just buy a Thunderbucker! Talk about sick tone!

[maxschrek]

Just buy a Thunderbucker! Talk about sick tone!

Hear hear, I second that!

[ThunderBucker]

Oh yeah, All good, I know...I should have called...Just was reminded of it. Any possibilities? The tone of these is sick??? Can it be duped???

well, this one is totally dead, if that is what you are asking.  Epoxy potted pickups are not very repairable.  But one coil is intact, so I should be able to get electrical measurements off of it, and the other is broken open so I can tell the wire type and size, take flux measurements on the ferrite magnets.  I should be able to learn quite a lot about it. It is a split coil, like a P bass, but the two coils share a common magnet up the center, then each coil has it's own magnet on the side.  It is an unusual design....

[TBird1958]

It's actually a cousin to a '76 pup IIRC, pretty sure I have another on the bench (amongst model train stuff!) at home.

[Bionic-Joe]

The '76's didn't have split coils......and they were sidewinders....

[TBird1958]

 
I gotta go do some looking, I recall one that I had which in essence looked just like this one except that it wasn't swimming in epoxy..........
And, I'm prepared to be completely wrong here too. 

[ThunderBucker]

Baz, here is your pickup report...
An unusual pickup design—two coils, each serving two strings, like a P bass.  But each coil is on the opposite pole of a central magnet shared by both coils.  And each coil has an secondary magnet mounted to the outside of the coil, which energizes one of the two pole pieces that each coil has.  So, a total of three magnets, four pole pieces, and 2 coils.

The two coils should be wired out of phase to cancel induced mag field noise, and since they are on opposite poles of the magnet, the string signals will still be in phase, like in all humbuckers.

In pix1, we see the central magnet, where the yellow paint is indicating the N pole of the magnet.  The 2 pieces of copper foil are to ground the steel pole pieces, so they will not pick up noise.  The foil wrap touches the steel at the interface between the central magnet and the pole piece . One coil was where all the damage is, and the other is at the other side of the magnet where you see the 2 steel pole pieces.

In pix2 you can see the secondary magnet, its purpose is to magnetically energize the lower of the two pole pieces (it isn't touching the central magnet, so it isn't energized by it—hence the need for another magnet).  Why not a single steel pole piece?  I suspect it is an attempt to reduce eddy current losses in the pole piece, tho I doubt it is necessary, and a single pole piece would make the pickup much easier to build.

In coil1 you can see the 2 pole pieces, the secondary magnet, and the copper coil wires.

Specs:

Central magnet:  Ferrite, .2" X .55" X 2.35"  ~140mT pole strength
Secondary magnet: Ferrite, .2" X .2" X 1.2" (about half as long 'cause it only covers one coil) ~110mT pole strength.
Pole pieces: cold rolled steel,  .062" X .7" X 1.135"
Bobbin: molded plastic, .385" tall, .56" wide, length over all 1.5".  Winding area .3" tall,.285" wide, 1.26" long.  Pole slot 1.13" long X .185" wide.
Coil: wound with AWG 44 solderable.  Intact coil measures  5.50Kohm, L 2.628H, Q 2.641 at 1kHz. (this is with the iron inside, raw coil would be lower L and Q).  I estimate between 4500 and 6500Turns. You'd have to wind one and sneak up on the final value.

Probably a pretty powerful and yet bright pickup.  The overall R would be about 10K (2 coils) and about 5.2H.  Not much losses due to the 2 pole pieces and the ferrite magnets (much less lossy than alnico)
Maybe not very warm sounding, ferrites tend not to sound that way.

[Bionic-Joe]

FANTASTIC!!!! Question is...Can you duplicate it???

[ThunderBucker]

Actually, I could probably fix this one, if you let me mill off the coil leftovers and buy me a spool of 44.  I don't use that gauge....

[Highlander]

Now that is hardcore...