The Molding Process and Identification of PAF Bobbins

The thermal injection molding process for PAF humbucker bobbins was carried out by Hughes Plastic Industrial, based in St. Joseph, Michigan, using three dual steel molds for bobbin production and an additional mold for M-69 mounting rings. These molds were finalized in January 1957. Each bobbin features a mold identifier and a chamber identifier, visible on the coil former, while M-69 mounting rings have their respective codes (and also the HPI logo) stamped underneath.

The first mold, CF-491-1, was used to produce screw bobbins with regular spacing. These were marked with CF-491-1 and chamber identifiers 1 and 2. The second mold, CF-490-2, was designed for slug bobbins with regular spacing, marked with CF-490-2 and chamber identifiers 3 and 4. The third mold was used for M-69 mounting rings, which produced both the short version (MR 491, marked with MR 491 and 7) and the tall version (MR 490, marked with MR 490 and 8).

The fourth mold, also labeled CF-491-1, was initially the first mold but was later refurbished to produce screw bobbins with narrow spacing. These narrow-spacing bobbins are marked CF-491-1, with 1 for the slug coil and 2 for the screw coil. The "CF" designation stands for "Coil Form," while "MR" refers to "Mounting Ring."

Vintage butyrate bobbins from this era often show tooling marks and minor imperfections, such as burrs at radius transitions, which are unique to each mold. When Gibson required an intermediate mounting ring for a three-pickup guitar, a tall MR 490 mounting ring was sanded down for use instead of the initially intended MR 493 design. An even shorter MR 492 was abandoned, which is why there are no parts numbered 5 and 6 until years later.

These small details are crucial for identifying original PAF components and understanding the production techniques of the time.

 

The Authenticity of M-69 Pickup Rings

M-69 pickup mounting rings, used for PAF humbuckers, are distinctive components easily identified by the mold markings on their undersides. These markings, a result of the injection molding process, indicate both the mold and model: bridge pickup rings are marked MR490, while neck pickup rings are marked MR491. Guitars originally equipped with PAFs featured either black or white M-69 rings. While black rings were more common, white rings were exclusive to Les Pauls, ES-295s, and select steel guitars, making them rare and highly sought after, often commanding unexpectedly high prices.

M-69 rings were made from Cellulose Acetate Butyrate (CAB), a thermoplastic cellulose ester known for its moderate butyryl content and low viscosity. Popular in the '50s, butyrate has since fallen out of favor. It is easily recognized by its distinctive odor, often described as sour milk or vomit-like.

To prevent cold joints during the molding process, the mold was gated. However, minor imperfections were introduced during the hand tooling of the original steel molds, leading to characteristic irregularities in the final molded parts. One notable feature is the oddly shaped screw funnel post on the bridge ring, a result of a repair made during the mold’s creation. These imperfections, along with subtle variations in texture, are key indicators of authenticity. Another distinctive characteristic is the half-moon-shaped ejector pin marks. Additionally, the rings’ signature bowed short ends are a natural consequence of the plastic’s shrinkage as it cooled.

The original M-69 rings possessed a distinctive flexibility, allowing them to conform to either flat or carved tops. Pickups were mounted using SAE 3-48 × 1" screws, nickel- or gold-plated to match the hardware, in combination with 1 5/8" steel springs for height adjustment. The rings themselves were secured with partially threaded #2 flat Phillips head screws, with two different lengths employed to suit the tall and short ring profiles. On black rings, these screws were chemically blackened. M-69 rings were fitted to Gibson guitars through 1969.

Between 1966 and 1967, Gibson used “generic” mounting rings due to a transition at its supplier. HPI moved to a new factory in 1966, upgrading its equipment and planning to retire old molds, including those for Gibson’s humbucker bobbins and mounting rings. As the transition progressed, HPI produced unmarked "generic" rings to bridge the gap before new M8 rings were introduced. In January 1967, a severe blizzard collapsed the roof of HPI’s new factory, delaying production for three months. This likely pushed back Gibson’s adoption of the new T-Top bobbins and M8 rings, which were finally introduced in early 1968.

 

Examining Butyrate Bobbins in PAF Manufacturing

The bobbins used in PAF pickups are made from Cellulose Acetate Butyrate (CAB), the same material used for M-69 mounting rings. Butyrate is a relatively soft material known for its unique resonance properties. Since these pickups do not use wax potting, the mechanical characteristics of the butyrate material subtly influence their microphonic behavior. Nonetheless, attempting to pot these pickups would be problematic, as CAB is highly sensitive to heat and prone to warping.

A few key mechanical specifications stand out. One notable detail is the slight difference in coil former sizes between slug and screw bobbins, even though they share the same outer dimensions. The nominal inner width of the bobbins is 1/4", with the E-to-E spacing measuring 1 15/16" (49.2mm), except in narrow-spaced PAFs. Another distinctive feature is the square-in-circle hole located on top and on the underside of the bobbin, through which the start lead wire passes. This design was originally required to fit the PAF bobbin into P-90 machine fixtures but was discontinued after the Patent No. era. In the non-adjustable bobbin, the hole is a larger circle with an offset square.

Butyrate bobbins typically lack a glossy finish and often show slight recesses between the poles, a result of material shrinkage during molding (CAB has a shrinkage factor of 2.5%). Due to the relatively soft nature of this material, butyrate bobbins can warp slightly under high winding tension.

Most PAF pickups were originally equipped with double black bobbins, although some feature one or both white bobbins. The use of white bobbins may have been due to a temporary shortage of black material or to fulfill orders for white mounting rings. These white-bobbin pickups first appeared in 1959, though they may have been produced earlier. 

Contrary to popular belief, there is no standard “zebra” or “reverse zebra” configuration, as the white bobbin can appear equally on either the slug or screw side. Gibson never defined a distinction between the two, and in company literature both versions were simply referred to as zebra without further clarification.

Over the years, players and collectors have attempted to impose a sense of order on this randomness. Some consider a pickup zebra only when the adjustable pole-piece coil is black, treating the opposite orientation as reverse zebra. Seymour Duncan, however, uses the exact opposite convention, defining zebra as a pickup with a white screw coil and reverse zebra as one with a black screw coil. Experts today may choose one naming scheme or the other, but historically no distinction ever existed.

PAFs with both white bobbins are especially valuable due to their rarity and association with iconic vintage burst players, and they have also become the subject of various legends. These pickups are not found on later PAF or Patent No. pickups, as their use was phased out after the early '60s. If a PAF retains its original cover and unaltered solder joints, the bobbin color can often be identified by inspecting them from the retaining screws.

T-Top bobbins were still made of butyrate and were exclusively black. They had thicker walls, making them stiffer. Unlike earlier bobbins, they lacked the 'square-in circle' holes. Their most recognizable feature was the molded 'T' on top, designed to ensure correct orientation and prevent incorrect installation.

 

Decoding the 'Vintage White' Color of Plastic Parts

While black is just black, light-colored plastics exhibit more complexity. The term "vintage white" is commonly associated with the distinctive off-white or ivory color found in vintage Gibson components, such as pickup rings and bobbins, made from Cellulose Acetate Butyrate (CAB).

Originally, CAB had a gently warm off-white tone. However, over time, photooxidation occurs when the material is exposed to ultraviolet (UV) light and oxygen. This chemical reaction breaks down the polymer chains in CAB, causing the plastic to gradually yellow or develop a cream-like discoloration. The rate of this process is influenced by factors such as sunlight exposure, handling, and environmental conditions, making each vintage piece unique in its aging process.

In contrast, Acrylonitrile Butadiene Styrene (ABS), the material commonly used for pickguards, ages differently. ABS undergoes oxidative degradation, leading to darkening, often taking on an amber or yellow hue over time. While modern plastics are engineered to resist these aging effects, these natural color shifts in vintage parts add their charm.

For guitar collectors and enthusiasts, the gradual transition of these components from their original color to cream or yellowed tones adds to the historical charm and character of vintage instruments. A fascinating effect of this aging process can be observed under a blacklight, where these components glow with a distinct hue, making it a useful tool for authenticating vintage parts.

 

The Authenticity and Function of PAF Covers

The vintage PAF humbucker pickup cover served both functional and aesthetic purposes, contributing to the classic look of these highly sought-after pickups while also enhancing their performance. Functionally, the cover shielded the coils from radio frequency interference and provided mechanical protection.

The original covers were produced by HPL Manufacturing Co., based in Cleveland, Ohio, using German nickel silver—an alloy composed of 60-65% copper for workability, 17-25% zinc for hardness, and 10-20% nickel for its silver-like appearance and corrosion resistance. The sheet stock used was initially 0.022" thick, which, after processing, measured approximately 0.021". Around 1959, Gibson transitioned to a thinner 0.020" material. The manufacturing process included deep-draw stamping, flush-cutting, belt-grinding, and wheel-polishing. These covers had a distinct shape, with flat faces, sharp side edges, rounded corners (reminiscent of old TV screens), and slightly recessed screw holes, often referred to as "dimples." Over time, the contours of these covers evolved due to die wear and variations in hand-finishing before nickel plating, with covers from the '60s displaying a softer shape.

The precise fit of the cover ensured a snug placement over the bobbins, minimizing susceptibility to feedback despite the absence of potting, resulting in only a slight increase in microphonics.

The low conductivity of nickel silver, coupled with the omission of a copper pre-plate in the electroplating process, helped preserve the pickup’s tonal characteristics. In contrast, gold-plated covers (24k gold over nickel) had a slightly greater impact on tone due to the inherent material properties of gold. In 1965, Gibson switched from nickel-plated to chrome-plated covers, aligning with a broader shift in the company’s hardware finishes. The plating process was handled by Bronson Plating in Kalamazoo.

Over the years, guitarists have debated the sonic differences between covered and uncovered PAFs. A covered, unpotted pickup introduces a subtle metallic overtone and "cluck," with the effect influenced by its proximity to the strings. Removing the cover slightly increases treble response and allows for closer pickup-to-string adjustment, enhancing perceived output and introducing a subtle thickening of the tone. Ultimately, the choice between covered and uncovered PAFs remains a matter of personal preference, balancing tonal transparency, resonance, and aesthetic considerations.

 

Understanding Alnico Variations in Vintage Pickups

Gibson’s PAF pickups are legendary for their unique tonal qualities, and one of the most fascinating elements behind their sound is the variation in the types of Alnico magnets used. The choice of Alnico grade, the length of the magnet, and even the inconsistencies in their production all played a crucial role in shaping the sound of these early pickups.

Alnico, an alloy of aluminum, nickel, cobalt, and iron, is well-regarded for its warmth, clarity, and smoothness. It was the most powerful permanent magnet of its time, which made it a popular choice for various applications, including electric guitar pickups. In the early days of PAF production, Gibson used a mix of Alnico grades, resulting in pickups that varied in sound. This variation contributed to the diverse tonal profiles that made each PAF unique.

Among these, Alnico 3 is notable as the weakest and rarest magnet found in vintage PAF pickups. Lacking cobalt, it produces lower output and a softer, less dynamic response, with reduced harmonic content. These characteristics made it less popular, and by 1957, it was phased out in favor of other grades.

Alnico 2, on the other hand, is cherished for its rich, smooth tones, featuring a scooped midrange and bell-like highs. It delivers a mellow, sweet sound with a softer low end, contributing to a smooth and slightly compressed feel.

Similarly, Alnico 4 offers a balanced tonal profile with a drier, more controlled response. It emphasizes the midrange while keeping treble and bass in check, making it a versatile choice.

In contrast, Alnico 5 is known for its brighter, more focused tone and increased output. It accentuates the midrange, providing excellent clarity and definition, particularly in the upper frequencies. The Alnico 5 crystals are aligned during the production process, exposing the material to a strong external magnetic field during or after casting. This alignment causes the magnetic domains to organize in a specific direction, enhancing its remanence (magnetic strength) and coercivity (resistance to demagnetization), ultimately improving the magnet’s performance. Its strong low end and pronounced highs create an aggressive, articulate sound without being harsh.

There is also an unoriented variation of Alnico 5, first identified in vintage PAF pickups from the late '50s through research by Tim Shaw at Gibson in the '80s. Shaw theorized that this variation resulted from an accidental heat treatment issue during production. Unoriented Alnico 5 retains similar magnetic strength to Alnico 2, offering comparable output but with a distinct tonal character. It produces a midrange-focused sound with a tighter low end and a sharper response, yet retains some of the smoothness of Alnico 2. This tonal difference is due to the variation in inductance profiles, giving unoriented Alnico 5 a crisper, punchier tone with a more dynamic presence.

Gibson used these magnets interchangeably, leading to natural variations in PAF tonal response. However, in 1961, the company standardized the use of shorter Alnico 5 magnets. While this transition was gradual and inconsistent—some early '60s models still featured long Alnico 5 magnets, and occasionally short Alnico 2 magnets—the change significantly influenced pickup performance.

The length of the magnets played a key role in shaping the PAF sound. Early PAFs used longer magnets, around 2 1/2 inches. However, by 1958, Gibson began using shorter magnets in some pickups. This change became more standardized in July 1961, when Gibson officially reduced the magnet length by approximately 1/8" or 1/4". The shorter magnets weakened the magnetic field, slightly lowering the pickup’s output, but the switch to Alnico 5 helped compensate for this. Generally, longer magnets produce a warmer sound, which is why late ’50s PAFs are still the most sought-after—shorter magnets became more common in later models.

An accidental occurrence in the world of PAFs is the flipped magnet bar, as seen in the famous 1959 Les Paul "Greeny". During a later repair, the magnet bar was mistakenly installed backward, reversing the pickup's polarity. This unintended modification resulted in a distinctive out-of-phase tone when both pickups are used together, making it a truly unique piece of rock history.

 

The Impact of Magnet Manufacturing on Tone

The magnet manufacturing process played a significant role in shaping the sound of the pickup. These magnets were rough-cast, meaning the alloy was melted at high temperatures and poured into molds made from fine sand. This method, known as sandcasting, resulted in magnets with a coarse, uneven surface. The texture of the sand, along with material irregularities from the cooling process, created small variations in the final magnet, contributing to subtle tonal roll-off.

Once the magnets were cast, they were magnetized in-house by Gibson using a method developed by Glen Seybert, an employee at the company. Initially, Gibson purchased uncharged magnets, which were more cost-effective. Seybert’s technique involved placing several magnets in a homemade magnetic charging block, creating a collective magnetic field that magnetized them all at once. While this method worked, it didn’t fully saturate the magnets with charge, leaving them weaker than magnets that had been individually magnetized. This led to some inherent inconsistencies in magnet strength, making some PAFs more powerful than others.

This magnetic marking system was a rudimentary method, which further contributed to variations in the strength and tone of the magnets. The North side of the magnets was marked with a felt-tipped pen.

Over time, Gibson sourced magnets from various suppliers, including General Electric's Carboloy plant in Edmore, Michigan, which became a significant source of Alnico magnets during the late '50s. Other suppliers included General Magnetics of Indiana and Allied Chemical, based in Chicago, Illinois. The quality of the magnets depended on both the materials and production methods, and fluctuations in sourcing sometimes led to differences in the final product.

The rough-cast, unevenly magnetized nature of these early PAF magnets gave each pickup its own character, creating the warmth, subtle complexity, and vintage charm that many players still seek today. The combination of material choice, production techniques, and natural inconsistencies are what truly set the PAF apart.

The practice of “magnet hijacking,” in which players place P-90 magnets into modern humbuckers to replicate the vintage PAF sound, has gained popularity. However, it’s essential to note that the final tone is shaped not only by the magnets but also by the winding of the coil, the placement of the magnets, and other production variables.

As PAF pickups age, many believe their sound evolves, particularly due to the magnets. While Alnico magnets can lose some strength over time, this decay is generally slow and minimal under normal conditions—only about 1-2% per century. Significant loss of magnet strength usually occurs only with exposure to extreme heat or strong magnetic fields.

 

The Role of Magnet Wire in Shaping the Sound

One of the defining elements of vintage Gibson PAF pickups is the use of 42 AWG (0.063mm) Plain Enamel magnet wire, also referred to as PE. This copper wire, coated with a thin layer of enamel insulation, was crucial in shaping the electrical and tonal characteristics of these iconic pickups.

This enamel insulation once common, was acetate-based and applied in a thin, uniform layer (single build). However, inconsistencies in coating thickness and even “warts” (raised imperfections) were common, leading to slight variations in wire properties. The color of the coating varied from dark orange to purplish brown. Unlike other types of magnet wire, the enamel insulation required mechanical removal before soldering, a process now replaced by solderable coatings in modern wire. While the primary purpose of the coating was to insulate the copper wire, its thickness and dielectric constant also influenced the coil's capacity, influencing the frequency response.

The copper wire was sourced from multiple suppliers, with International Wire Group (IWG) being one of the largest. The copper used then was not as refined as today's, with variations in purity and composition due to less strict manufacturing standards. The processes of drawing and annealing— where the wire is stretched and heat-treated to adjust its properties—were less controlled than today's methods, leading to subtle differences in resistance, ductility, and diameter. These variations in copper processing contributed to the unique tonal qualities of the pickups, as even slight changes in the wire’s characteristics could affect the electrical behavior.

These subtle variations in wire diameter, coating thickness, and resistance “per foot” influenced the final tonal output, contributing to the distinctive sound of vintage PAFs. In 1963, Gibson transitioned to poly-coated wire, marking a shift from the characteristics that made these early pickups so revered. This change was driven primarily by production efficiency, as poly-coated wire was easier to work with.

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The Construction and Winding Process of a Vintage PAF

Gibson originally wound each PAF guitar pickup using the same wire as their P-90 pickups. A typical PAF consists of two bobbins, each wound with approximately 5,000 turns of this wire. However, the actual number of turns could vary due to inconsistencies in the winding process. Some machines lacked stop counters or had malfunctioning ones, which led to slight underwinding in some cases, while others were overwound by as much as 1,000 turns—particularly in the late '50s. As a result, the DC resistance (DCR) of vintage PAF pickups varies widely. Some pickups are notably hotter than others, and many exhibit moderate coil mismatches. A mismatch in turns—often up to a few hundred—can enhance the treble response without affecting hum cancellation. Higher DCR can also result from higher resistance per foot of wire or increased winding tension (due to greater pressure from the machine’s felt tensioners, which stretch the wire). Contrary to popular belief, most PAFs are not drastically far off their intended winding specifications.

Unlike Fender pickups from the same era, all P-90 and PAF pickups were machine-wound. An automatic transverse guide ensured even wire distribution across the bobbin, minimizing wire scattering compared to manual winding. This method also resulted in lower coil capacitance due to the reduced overlap of the windings, contributing to a brighter tone. However, the interior of a PAF’s coil often appears uneven. The start lead wire runs internally into the bobbin, winding around the plastic former and obstructing the path of the magnet wire. This interference causes the inner layers of the coil to be less compact, contributing to the enhanced microphonics characteristic of vintage PAF pickups.

The lead wire for both the start and end of each coil is a 7-strand, 28 AWG tinned copper wire with black PVC insulation. The start of the screw bobbin is soldered to the nearest corner of the baseplate, while the start of the slug bobbin is soldered to the core of the output wire. These two coil ends are then connected. In later Patent No. pickups, the coil leads were color-coded black and white, with the end wire marked white to prevent confusion with the start, as the start wire was repositioned externally and no longer passed through the bottom hole.

To protect the coils and soldering, a 1/4" black flatback paper tape is applied. A small piece of 1/2" tape (or sometimes two 1/4" pieces) covers the side with the lead wires. This tape, known as 3M’s Scotch #4 Tape, is recognizable by its black adhesive and olive-green color under blacklight. Notably, this tape is no longer in production. The solder used was the common lead-tin alloy, due to its relatively low melting point and good conductivity.

In a Gibson humbucker, both coils are wound counterclockwise when viewed from above. The coils face the opposing poles of the magnet bar, with the screw side facing the south pole. In the PAF design, the side with the lead wires is opposite the baseplate hole where the output wire exits, with the wire running along the edge.

During the Norlin years, Gibson began wiring the leads on the same side as the hole to save on braided wire length. Some pickups even used gray PVC multi-conductor wire. Another change from this period was the switch from a single maple spacer under the slug bobbin to two white plastic spacers.

The absence of paraffin potting in vintage Gibson pickups allows the coil windings to resonate naturally, enhancing harmonic content and producing a richer, more dynamic tone. This results in a unique, organic character with increased sensitivity to a player's touch. While slightly more susceptible to feedback, their solid construction helps keep it under control. Additionally, wax potting introduces capacitance, which further alters the tone.

 

The Machines Behind Gibson's Iconic Pickups

The creation of PAF pickups was significantly influenced by the machines used to wind their coils, a total of four: the Gibson Seybert Winder, the Geo-Stevens 115, the Leesona 102, and the Meteor ME-301. While these machines hold historical relevance, it was the winding process itself—rather than the machines' features—that played a key role in shaping the PAF's iconic tone. While many believe PAFs were hand-wound, no original PAF pickups were—except for rewinds of old coils.

The Gibson Seybert Winder is a vintage pickup-winding machine dating back to the 1930s, originally manufactured by Crown in Illinois. It was first used to manually wind large diagonal pickups, such as those found in the 1940 ES-300 guitars and possibly the Charlie Christian pickups from the same era.

In the '50s, Glen Seybert modified the machine into an auto-traverse pickup winder by adding a wooden wire guide and tension mechanism. These modifications, which included period-typical parts like cream-colored strap buttons used as wire guides, were likely made to increase the production of the newly introduced PAF pickups, allowing the machine to meet growing demand.

Powered by a separate electric motor, the winder’s unique drive system causes the winding mechanism to move unevenly, slowing down as it nears the end of its traverse. This results in a distinctive hourglass-shaped coil, setting it apart from other winding machines.

The winder was designed to wind four slug bobbins at a time, but it could not accommodate screw bobbins. Although it could have been fitted with a necessary tailstock fixture, this upgrade was never implemented.

Due to its exclusive use of slug coils, unique winding pattern, and the absence of a stop counter, PAF pickups produced on this machine tend to have a distinct tonal character. While it was eventually retired, its impact can still be heard in some vintage PAFs.

The Geo-Stevens 115 pickup winder has a notable history, first entering the Gibson factory in Kalamazoo in 1950. Built by Geo-Stevens, it was originally ordered by industrial supply company Allen Electric & Equipment. This machine played a crucial role in the production of PAF and P-90 pickups, featuring unique fixtures that limited wire traverse, resulting in a coil with more scatter and a "center-focused" design.

Although the machine achieves an optimal Turns Per Layer (TPL)—calculated by dividing the bobbin width by the wire’s outer diameter—its shorter wire travel produces a fatter coil with fewer turns of 42 AWG wire. This results in a warmer, low-end tone. A few hundred extra windings fully pack the bobbins, widening the magnetic aperture. Notably, the machine was not equipped with a stop counter.

In 1956, its motor was replaced, and it continued winding PAF and P-90 bobbins at the Kalamazoo factory. Later, as Gibson transitioned to Nashville, Les Paul himself rescued the machine, though it remained unused for decades. In 2015, it was sold at auction and later acquired by Throbak, which also owns the original Gibson Seybert Winder.

Still bearing the wear marks from winding countless PAF and P-90 bobbins, the machine remains a legendary piece of pickup history.

The Leesona 102 holds a special place in the world of PAF pickups. Known for its precision winding, this machine is highly regarded by enthusiasts. Like the Geo-Stevens machine, it produces an optimal TPL, but its unique design featuring a lobed cam allows for a more even distribution of wire, resulting in a more consistent coil shape.

Originally built by the Universal Coil Winding Company, the Leesona 102 was designed as a versatile industrial coil winder, capable of handling coils from 3” down to as small as 1/32”. Its most notable feature is its lobed cam, which enables a smoother wire traverse and a more uniform winding pattern. This precision contributes to the unique tonal signature of PAF pickups—rich and full-bodied, with a balanced low end and clear mids. Compared to the Geo-Stevens 115, the Leesona’s coils tend to be more uniform and less "scattered," resulting in a slightly more defined midrange response.

In the early '50s, Gibson began using the Leesona 102, marking a turning point in PAF production. This machine played a crucial role in creating Gibson’s iconic pickups and was also used by companies like Rowe Industries for their DeArmond pickups. Though originally built for various industrial applications, its ability to wind exceptional-sounding guitar pickups cemented its legendary status in vintage gear history.

The Leesona 102 features a three-station setup with an adjustable traverse, making it well-suited for winding different pickup models, including the PAF. It was more efficient than other machines of its time, offering smoother and faster production. However, its size and weight led to many units being discarded as scrap in the early '90s. As a result, the Leesona 102 is now extremely rare, with only a handful of operational models remaining.

While renowned for its quality, the Leesona 102 wasn’t without quirks. The adjustable traverse, though versatile, introduced slight inconsistencies in the winding process at the smaller settings. The counters were also prone to failure.

With its rich history and rarity, the Leesona 102 is more than just a tool; it’s a vital piece of the legend surrounding the iconic PAF pickups. Of the two original machines used by Gibson, both are now owned by Seymour Duncan, though only one—modernized—remains operational.

The Meteor ME-301, often regarded as the most efficient PAF pickup winder, holds a unique place in Gibson’s winding history. Unlike other PAF winding machines, the ME-301 combines low wire tension, a highly accurate traverse, and a TPL setting of 65—lower than optimal. These characteristics result in consistently wound coils that are fuller and slightly warmer in the low end compared to those wound on the Leesona 102.

A Swiss-made machine, the ME-301 was designed with production efficiency in mind. Dating back to the '50s, it is still in use today at the Gibson Pickup Shop, though modern modifications have removed its original Meteor wire guides to accommodate more bobbins per machine. Its quick-change chuck system allows operators to swap fixtures rapidly, making it well-suited for mass production.

What sets the ME-301 apart tonally is its approach to TPL adjustment. Rather than requiring manual fine-tuning, the machine features a large dial where the operator simply selects the wire gauge. For a PAF coil, turning the crank to 42 AWG wire automatically sets the TPL to what should be the most efficient setting. However, every ME-301 ever built has this setting calibrated 35% lower than optimal, creating a distinct winding pattern that defines the sound of pickups wound on this machine. If adjusted while running, the friction disc that controls the TPL will undergo excessive wear. A worn friction disc will cause a significant TPL deviation.

This unique winding characteristic makes ME-301 coils instantly recognizable in vintage pickup repairs. It was used to wind not only PAFs but also P-90s, mini-humbuckers, and later Kalamazoo-made T-Tops.

The ME-301’s combination of efficiency and distinctive winding characteristics has solidified its legacy as a key player in the production of Gibson’s legendary pickups. Even today, its impact continues to be heard in the warm, balanced tones of the guitars it still helps to shape.

 

The Small Parts That Shape Humbucker Tone

The smallest components of a PAF humbucker—pole screws, slugs, and the keeper bar—play a vital role in shaping the pickup’s tonal characteristics. These parts contribute to the magnetic circuit, transferring magnetism from the Alnico bar magnet to the strings. Their material composition, geometry, and manufacturing precision all influence the pickup’s response, dynamics, and harmonic complexity. Each component serves a unique function in defining the PAF’s tone. The steel grades used for the pole screws and slugs directly impact the pickup’s overall sound. Additionally, the way these parts are manufactured and assembled is crucial to preserving the legendary PAF tone.

Originally produced by Watkins Machine Shop in Kalamazoo, Michigan, the materials used in PAF pickups remained consistent throughout their production. Lab tests on vintage samples confirm that the material chemistry did not change during this period.

One of the most important small components in a PAF pickup are the pole screws. Each PAF features six slotted, 5-40, 3/4" fillister head, nickel (or gold) plated pole screws that are adjustable. These screws enable precise fine-tuning of the string response by raising or lowering them. The steel composition of these screws directly influences the treble frequencies.

Vintage pole screws typically have a lower carbon content, ranging from 1006 to 1018 steel grades. This results in a smoother, less aggressive treble response compared to modern counterparts, which generally feature higher carbon content. Additional details about these screws include a short 'cheesehead' profile with a rounded top, non-tapered threads, and an indentation at the end. Furthermore, the head cut may sometimes be slightly off-center.

In addition to the adjustable pole screws, slugs are crucial for completing the magnetic circuit. These nickel-plated steel slugs are pressed into the bobbin on the side facing the north pole of the Alnico magnet. Made from 1215 steel—a material selected for its superior machinability and ability to be cut without lubricants—slugs still require the most complex production process. The cutting process, carried out on a Brown & Sharpe machine, often left a distinctive bullseye pattern on the surface.

The specific steel composition of the slugs significantly influences the pickup’s response, helping to reinforce the balanced tone that characterizes a classic PAF. A hard maple spacer is positioned on the side opposite the magnet-facing side of the slugs, stabilizing the bobbin and ensuring its structural integrity.

Another vital component is the keeper bar, a precisely cut steel piece that is machine-flattened on both sides and drilled with ten holes to accommodate the pole screws and bobbin mounting screws. It serves two primary functions: maintaining the charge of the Alnico magnet and stabilizing the bobbin on the baseplate.

The keeper bar is made from cold-rolled 1016 steel, a material that is no longer in production. This particular grade of steel offers an excellent balance of magnetic permeability and machinability, making it an ideal choice for its role in the pickup’s magnetic circuit. The low carbon content of 1016 steel allowed it to maintain good magnetic efficiency, enabling the efficient transfer of magnetic flux between the magnet and the pole screws, which played a crucial role in optimizing the pickup’s overall performance.

Though often overlooked, these small components are critical to the PAF’s tonal characteristics. Their metallurgy, manufacturing precision, and assembly process all contribute to the distinctive sound that has made vintage PAFs highly sought after. These materials and design choices continue to uphold the legendary status of these pickups.

 

The Anatomy of a PAF Baseplate

The PAF baseplate is a crucial component of its legendary design, serving as both the structural foundation for the pickup assembly and a key influence on its tone. Produced by Watkins Machine Shop from 1/2-hard nickel silver alloy, the baseplate provides tonal transparency, unlike the zinc-plated brass baseplates of P-90 pickups, and readily accepts solder, ensuring a solid connection for the pickup cover. It also serves as the primary grounding point, with the braided shielded wire soldered to it.

Its threaded legs allow height adjustment screws to secure the pickup to its mounting ring, and the distinctive "L"-shaped tooling marks in the feet, left from the stamping process, help authenticate a vintage PAF. Unlike modern humbuckers, vintage PAFs feature pole screws that thread directly into the baseplate, creating a solid mechanical structure. This design enhances tonal clarity and resonance while minimizing feedback issues. These elements contribute to the clarity, resonance, and dynamic character that make vintage PAF pickups so highly sought after.

At the bottom of the baseplate, four small Phillips-head brass wood screws secure the bobbins. These #2 x 1/2" partially threaded screws are distinctive in shape, with brass chosen for its non-magnetic properties, ensuring minimal interference with the pickup's magnetic field. While brass screws are standard, a few verified vintage examples feature steel screws of identical shape, highlighting occasional manufacturing variations in these iconic pickups.

Soldered to the baseplate is a 22 AWG two-conductor hook-up wire manufactured by Belden. This wire features a 2-strand braided metal outer wrap and contains seven individually tinned copper strands twisted together. The strands are then encased in Celanese nylon-type insulation, followed by a waxed black cotton overbraid. Notably, this wire exhibits lower capacitance compared to modern 3-strand counterparts, contributing to the characteristic tonal properties of vintage PAF pickups.

The PAF decal is a waterslide decal made of cellulose, featuring ink-stamped lettering and a silkscreened "Patent Applied For" text in oil-based gold ink. The letters are uniquely spaced, not from a standard font, giving the decal a hand-made appearance. Due to the delicate materials and aging process, original decals often show wear, flaking, and the edges tend to yellow over time. This decal is a key identifier of vintage PAF pickups with historical significance, and it often appears off-center or even upside down. The later Patent No. decal was made using the same process.

 

Written by Giuseppe Fumuso