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’Bucking Hum and Then Some

I was recently put in a position where I had to know a great deal about PAF pickups. Like most guitar players, I have a tendency to say “I can

I was recently put in a position where I had to know a great deal about PAF pickups. Like most guitar players, I have a tendency to say “I can fake my way through it,” but the stakes in this case were way too high to not be honest with myself. So off I went to the woodshed with the intention of learning everything I could about PAFs. I will fill you in on why I put myself through this endeavor later, but I first want to pass along the essential knowledge I learned in the process.

So I don’t lose anyone at the bakery, let’s begin with humbucker basics. In any magnetic pickup, a vibrating guitar string induces an alternating voltage in its coils. However, magnetic coils are also antennas and are therefore sensitive to the electromagnetic interference that can be generated by wiring and various electrical appliances. Guitar pickups collect this noise, which can be quite audible, sounding like a constant hum or buzz.

A humbucker has two coils with opposing windings and polarities. The string motion induces current in both coils in the same direction. Electromagnetic interference, on the other hand, induces current in opposing directions in each coil because of the reversed winding and polarity. When the signals from both pickups are combined, the noise is cancelled and the actual signal is increased, dramatically improving the signal- to-noise ratio. This technique is called common-mode rejection by electrical engineers and is also used for balanced lines in audio recording.

Before the invention of the humbucker, guitarists relied on single coil pickups, like Gibson’s P-90, which did nothing to block the dreaded 60-cycle hum. In the mid 1950s, Gibson engineer Seth Lover was assigned to tackle this problem. Seth connected two single coil pickups in series, as opposed to parallel, and connected the coils out-of-phase, both electrically and magnetically – thus the signal noise of one coil canceled out that of the other, which is ultimately how the pickup came to be known as “humbucking” or humbuckers. Seth and Gibson filed their patent for the pickup design on June 22, 1955, and Gibson added the new pickups to steel guitars in 1956 and on electric solidbody and archtop guitars – including the Les Paul Model – in 1957. During late 1957, a small black decal with gold lettering was added to the underside of the pickup that read, “PATENT APPLIED FOR” and the PAF designation was born.

Each humbucker has a bobbin wound with a certain type of wire. On original PAFs the bobbin wire appears purple, versus later PAFs that have a reddish appearance. Additionally, different types of wires had unique coatings. When wire coatings change, the sound of the pickups also change. The amount of wire and coating wound on each bobbin helps to determine the pickup’s resistance. When the bobbins are wound with more than a nominal amount of wire they become more powerful, offering fatter midrange at the expense of treble response. The people running the pickup winding machines used by Gibson from 1956-1961, whether knowingly or unintentionally, were inconsistent with the numbers of windings. The machine operators essentially estimated when a pickup bobbin reached 5000 turns of wire, which ended up giving each set of PAF pickups a unique sonic character.

I had to learn all this info because Larry Carlton wanted to replace the original humbuckers in his number two 335, a ‘68 that has been previously used as the backup guitar for his famous ‘69 model, played on over 200 number one hits. Knowledgeable techs told me to look for the “PATENT NO.” style with unopened nickel-plated covers, or, better yet, a pickup with the “PATENT APPLIED FOR” decal intact, which are highly valued and harder to find. Here is what I was specifically looking for: original PAFs made in 1956 or 1957 that had a long magnet, no PAF sticker, purple bobbin wire, black leads on both coils, brushed stainless steel covers, Phillips screw bases, ohms ranging from 7k to 9k, black PAF-style bobbins, and L-shaped tool marks on the feet; original long-magnet PAFs made from 1957 to 1960 that had “PATENT APPLIED FOR” stickers, purple bobbin wire, black leads on both coils, nickel covers, Phillips screw bases, ohms measuring from a low of 7k to a high of 9k ohms, black PAF-style bobbins and L-shaped tool marks on the feet; or a set of the final batch of PAFs made in ‘61 or ‘62 that featured a short magnet, “PATENT APPLIED FOR” sticker, purple wire, black leads on both coils, nickel covers, Phillips screws on the base, double black bobbins and the L-shaped tool marks.

I knew if I found any of these and their measurements were good, we were in business. Lo and behold, we found a matched set made in 1960 and put them in the ‘68 335. They sound amazing. Lately, Larry has been touring with “number two” exclusively, due to the sound of those pickups. It was a great learning experience for me and the end result was that the world gets even more from Mr. 335 himself, which we can all enjoy.

Rick Wheeler
Rick Wheeler currently works as Larry Carlton’s guitar tech and front of house engineer. He is also an accomplished jazz guitarist, vocalist, and educator. You can contact Rick at