Anatomy of a single coil (Courtesy of Seymour Duncan)
Excluding those economic, the pickup magnets of the Stratocasters are made of AlNiCo, an alloy consisting of Aluminum, Nickel and Cobalt to which a variable amount of iron is added. According to the different percentage of the single elements which form it and to its attractiveness, alnico can be cataloged numerically from II to IX.
It is common opinion to consider alnico III the material used for the magnetic poles of the Stratocasters made between 1954 and 1955 and the more powerful alnico V for the Stratocasters that have been built since 1956. However, the alnico used by Leo Fender in the '50s and '60s was different from the current Alnico III or Alnico V, because the percentage of the main constituent elements and of the impurities was different from that of the most recently produced magnets, reason why in reference to vintage Stratocasters, it would be preferable to speak only of "Alnico".
Obviously, it's not just the composition of the magnets that characterizes the sound of the pickups: all the materials that make them up, the size of the magnetic poles and the windings are decisive for the final result.
It is common opinion to consider alnico III the material used for the magnetic poles of the Stratocasters made between 1954 and 1955 and the more powerful alnico V for the Stratocasters that have been built since 1956. However, the alnico used by Leo Fender in the '50s and '60s was different from the current Alnico III or Alnico V, because the percentage of the main constituent elements and of the impurities was different from that of the most recently produced magnets, reason why in reference to vintage Stratocasters, it would be preferable to speak only of "Alnico".
Obviously, it's not just the composition of the magnets that characterizes the sound of the pickups: all the materials that make them up, the size of the magnetic poles and the windings are decisive for the final result.
Windings
While keeping the same copper wire gauge (AWG42, which corresponds to about 0.063mm), Fender modified the winding method over the years. Until 1964 pickups were wound by hand (a system called scatter winding or hand winding) by means of a small belt-driven wrapping machine that counted the number of turns. As it was not a machine-controlled work but a manual one, the tension applied during the winding could vary within the same pickup and between different pickups, and not infrequently the copper wires were wound irregularly, thus determining important differences among the pickups. The number of windings therefore ranged between about 8000 and 8700 (reason why 8350 is often considered the standard number of windings of an old pickup).
With the advent of CBS in 1965, modern automatic winders gradually replaced hang-guided wrapping machines, with the result of obtaining more regular turns, in which the copper wires were parallel to each other, but whose tension was lower, as applying a larger one without direct manual control could have broken them. Consequently, the number of windings decreased a lot and remained constant around 7600 over the years, its diameter increased (because they were under a lower tension) and the length of the copper wires decreased, directly affecting the resistance: the new pickups, in fact, exhibited a slightly lower output.
With the advent of CBS in 1965, modern automatic winders gradually replaced hang-guided wrapping machines, with the result of obtaining more regular turns, in which the copper wires were parallel to each other, but whose tension was lower, as applying a larger one without direct manual control could have broken them. Consequently, the number of windings decreased a lot and remained constant around 7600 over the years, its diameter increased (because they were under a lower tension) and the length of the copper wires decreased, directly affecting the resistance: the new pickups, in fact, exhibited a slightly lower output.
Magnetic Poles
In 1954 the Stratocaster magnetic poles were slightly beveled on the edge and staggered following the ascending order: B, E (treble), G, E (low), A, D; since 1956 the magnet of the G string has become the higher one. Their diameter could vary from 47mm to 50mm.
Since the end of 1974, as a consequence of an increasing use of smaller string sets than those previously used, the magnetic poles had been no longer staggered but all at the same height (flush poles).
Until 1957 the polarity of the poles was south. Since 1958 pickups with north polarity had gradually begun to replace the previous ones, which, however, can be found until around 1959.
Since the end of 1974, as a consequence of an increasing use of smaller string sets than those previously used, the magnetic poles had been no longer staggered but all at the same height (flush poles).
Until 1957 the polarity of the poles was south. Since 1958 pickups with north polarity had gradually begun to replace the previous ones, which, however, can be found until around 1959.
Black & Grey Bottom
Until the first half of 1964, Stratocaster single coils featured a black vulcanized fiber bottom plate and top - reason why they are nicknamed Black Bottom - and the windings had an intense copper color due to the formvar (poly vinyl formal varnish) insulation, a polyvinyl resin. With the aim of eliminating a possible source of microphonic noises, they were dipped in hot wax bath, a process known as wax potting. The screws were wrapped in small elastic rubber tubes.
Since March 1964, the Black Bottoms had begun to be gradually replaced by the new Grey Bottom pickups, characterized by a grey bottom plate (at first light and slightly darker from 1968), which finally replaced them at the end of 1967. The windings of the new pickups were burgundy color due to the new insulating coating, plain enamel (already used by Fender in the 1950s).
Their screws "springs" were not made out of rubber, as in the Black Bottom, but they were real metallic springs.
However, also in the '70s it is possible to find Black Bottoms because, in order to run out of stock, undated pickups with black fiber bottom plates were made.
Unlike the pickups used previously, the Gray Bottoms were not always immersed in wax, but they were lacquer potted, a process that had to be done during the winding as the lacquer did not penetrate deeply into the coils. In the '70s the lacquer potting was sometimes done too late (or it was not done at all), and the result was the frequent production of microphonic pickups. For a long time it was not possible to understand the nature of this problem, which was solved only in late 1981 thanks to Dan Smith.
In the late '70s Fender gradually began to prefer polysol insulating coating, and gradually, from 1980, black plastic top and on bottom plates.
Since March 1964, the Black Bottoms had begun to be gradually replaced by the new Grey Bottom pickups, characterized by a grey bottom plate (at first light and slightly darker from 1968), which finally replaced them at the end of 1967. The windings of the new pickups were burgundy color due to the new insulating coating, plain enamel (already used by Fender in the 1950s).
Their screws "springs" were not made out of rubber, as in the Black Bottom, but they were real metallic springs.
However, also in the '70s it is possible to find Black Bottoms because, in order to run out of stock, undated pickups with black fiber bottom plates were made.
Unlike the pickups used previously, the Gray Bottoms were not always immersed in wax, but they were lacquer potted, a process that had to be done during the winding as the lacquer did not penetrate deeply into the coils. In the '70s the lacquer potting was sometimes done too late (or it was not done at all), and the result was the frequent production of microphonic pickups. For a long time it was not possible to understand the nature of this problem, which was solved only in late 1981 thanks to Dan Smith.
In the late '70s Fender gradually began to prefer polysol insulating coating, and gradually, from 1980, black plastic top and on bottom plates.
Dating
Both the last Black Bottom pickups and the very first Grey Bottoms could be dated, and the date of production could be found on at least one of the three pickups.
- Since the beginning of 1964 Fender had begun to date, by a yellow stamp, the bottom plate of its last Black Bottom pickups (ex.: JAN 11, 64); however, in early 1964 it is possible to find also some date written with a white pastel.
- In the same period also the new Gray Bottom pickups began to be dated: the very first with the same yellow stamp used for the Black Bottoms, the subsequent by hand (ex.: 1-15-64), pencil, or marking pen. Sometimes the initials of the worker who had wound them could also be present.
- Since 1969 this date had begun to be printed by a black stamp. It seems that the date was sometimes reported in full, written in numbers, but some pickups show a code that seems to invalidate this theory; moreover, it doesn’t always coincide with the exact date of production (but only with the year). In any case, the last number refers to the year of production of the pickups (ex.: "128 9" for a pickup of 1969 or "1405 78" for one of 1978). In particular, the dates on pickups are useful to date the Stratocasters of the '70s with no date on the neck.
- The pickups with bottom and top plates in black plastic used from 1980 by Fender were no longer dated, but they only featured the code "016730".
Some 1964 single coils featured a yellow stamped date (courtesy of Nino Fazio, realvintage.it)
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1960 Black bottom pickups
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Gray bottom pickups (courtesy of ReCaster)
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"Rubber" springs
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Formvar (right) vs Plain Enamel (left)
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The '80s
Red bottom pickup
The 1980 Strat featured the new X-1 pickup at the bridge, which was also used on 1981 on the Stratocaster Standard known as "Smith Strat", with a greater resistance (7,5kΩ), recognizable because most of the time equipped with a cable covered with a yellow plastic.
The Stratocaster Elite was equipped with weak pickups in Alnico II to compensate its active circuit. In addition, between the pickup at the bridge and the central one, it featured a dummy coil to obtain a hum reducing.
The Vintage reissues, unveiled in 1982, featured pickups with staggered poles. On the very first made, in 1982, sometimes Red Bottom single coils could be used, and they could be considered premium pickups. The red bottoms of the first Vintage reissues had the date printed on the bottom plate.
The Lace Sensor pickups of the Plus Series were completely different and deserve a separate chapter.
The Stratocaster Elite was equipped with weak pickups in Alnico II to compensate its active circuit. In addition, between the pickup at the bridge and the central one, it featured a dummy coil to obtain a hum reducing.
The Vintage reissues, unveiled in 1982, featured pickups with staggered poles. On the very first made, in 1982, sometimes Red Bottom single coils could be used, and they could be considered premium pickups. The red bottoms of the first Vintage reissues had the date printed on the bottom plate.
The Lace Sensor pickups of the Plus Series were completely different and deserve a separate chapter.
