By the mid-1950s, Gibson wanted to counter the latest electric guitars introduced by competitors and especially those by Fender. Leo Fender had built a company from nothing in the mid-1940s to a substantial factor in the solid-body guitar market. Gibson believed they could beat Fender and other rivals for market share by developing a low-noise pickup.
Players loved the sound of Gibson's P-90 and Fender's single-coil pickups, but they also put up with the 60-cycle hum (noise) inherent in their respective designs.
Gibson's management assigned this important task to one of their engineers, the late Seth Lover. Seth's subsequent design and patent changed guitar playing and music recording history. Let's leave the heavy technical discussion for another article and understand the basic design: Seth connected two single coil pickups in series. However, he connected the coils out-of-phase electrically and magnetically. Thus, the signal is passes through the pickup minus much of the noise or hum. That is how the pickup Seth designed came to be known as the humbucker.
Seth's pickup patent was filed on June 22, 1955. Gibson added the new pickups to steel guitars in 1956, and in 1957 on electric solid-body and arch-top guitars, including the popular Les Paul Model. During 1957, a small black decal with gold lettering was added to the underside of the pickup. This decal read, "PATENT APPLIED FOR". Later, as the vintage guitar market evolved from savvy recording artists to local musicians, these pickups became known as the 'PAF'.
Seth Lover received his approved pickup patent, #2,896,491, on July 28, 1959. By late 1962, Gibson changed the decal to read, "PATENT NO 2,737,842". It is interesting to note that the patent number listed on the decal was not for the pickup design, but for Les Paul's trapeze tailpiece. One can assume Gibson was creating a research roadblock for the competition. Or, was it simply a typo? The competition idea seems more credible, but silly, as these new decals appeared 7 years after the pickups were first installed on Gibson's instruments.
Between 1959 and 1960, Gibson made PAF pickups with white and black plastic bobbins. Prior to this point in time, both of the bobbins were black. These oblong bobbins are exposed when the pickup's metal cover is removed. Thus, some PAFs are referred to as double black (two black bobbins), zebra (one black and one white bobbin) and double cream (two white bobbins). Because collectors and players want the rarest possible instruments, amps, parts, etc... Vintage double cream and zebra PAFs command higher prices that the more common double black pickups. These variations of PAF pickups with cream bobbins are also in their prime period of construction from 1956-1960. The bobbin's color does not influence the sound of the pickups. It's purely cosmetic, but creates a very cool image.
From 1956 until sometime in 1961, Gibson used different Alnico magnets in their PAFs. Alnico magnets (composed primarily of the alloys ALuminum, NIckel, and CObalt) come in a variety of grades based on their magnetic strength. Gibson used the same magnets (size and grades) available for their P-90 pickups. It seems Gibson randomly used Alnico 2, 3, 4 and 5 grade magnets in PAFs until 1961. The higher the magnet's number, the higher the magnetic strength. By 1961, Gibson began consistently using a smaller size Alnico 5 magnet. Generally speaking, decreasing the flat (top) side size of these magnets decreases the power of the pickups.
As for wiring, Gibson used a braided shield wire for connection to the control pot. The pickup bobbins were wound with #42 (plain enamel) wire. The bobbin wire appears purple versus later versions that appear reddish. Gibson eventually switched to polyurethane coated wire around 1963. The capacitance of the coating is determined by thickness and material composition, and this influences the sound of the pickup. When coatings change, the sound signature of the pickup can change.
The amount of wire (and coating) wound on each bobbin determines the DC resistance and other factors, including sound characteristics. When the bobbins are wound with more than a nominal amount of wire, the more power they exhibit, thereby sounding fatter in the midrange with less treble. The resonant peak of the pickup changes as more or less wire is used. Due to human intervention and the wide-tolerance of the winding machines and the test equipment used by Gibson from 1956-1961, PAF pickups during these years usually measure between 7.5 - 9.0 thousand ohms (K ohms).
Thumbs up to the late great Seth Lover!