Phase of a humbucker?

[Lyrebird Steve]

Rob: I'm putting these links here so I can find them again when I need them

How Hum Cancelling Works
How Hum-Cancelling Works, Part 1 | Seymour Duncan Blog
How Hum-Cancelling Works, Part 2 | Seymour Duncan Blog

How Humbuckers Work
Guitar Wiring Site - How A Humbucker Works

[Mike Sulzer]

Rob: I'm putting these links here so I can find them again when I need them

How Hum Cancelling Works
How Hum-Cancelling Works, Part 1 | Seymour Duncan Blog
How Hum-Cancelling Works, Part 2 | Seymour Duncan Blog

How Humbuckers Work
Guitar Wiring Site - How A Humbucker Works

That seems like a good solid explanation of hum cancelling. This needs some clarification:

However, the coil will also pick up disturbances in ambient magnetic fields around the guitar.

Once you have stated that there are ambient fields, you have lost any reason to talk about disturbances. They simply are what they are. The field from that leaky old power transform is inherently ac (changing in magnitude and sign). Nobody is disturbing it; it is ac in nature and the changing flux through the pickup coil induces a voltage. 'Disturbing the field" seems to come from a misunderstanding of the changing magnetic reluctance in a so called magnetic circuit. However, that cannot possibly work here. No reluctance is varying; there simply is a time varying field and it induces a voltage. The whole purpose of a field is to allow the effect of a source to be determined in a convenient way. In the case of the transformer, it is not necessary to consider the motion of each electron in the winding and the state of each atom in the core. The field is a convenient description of what happens.