All pickups have bobbins. The coils are formed onto the bobbins, plus they hold the pole pieces in position. Traditionally single coil bobbins were made of compressed fiberboard and many still are. Bobbins using fiberboard have a top and bottom plate and are pressed onto the pole pieces which act as an integral part of the bobbin structure. The magnet wire is wound directly around the row of pole pieces and held in place by the fiberboard plates.
Humbucker bobbins were originally made of butyrate; a type of plastic available during the 50’s when they were first in production. Modern plastics are used these days for humbucker bobbins, and also for many single coil bobbins. The choice of materials for bobbins all have one thing thing in common: They are not made of metal and the materials used have no influence on the magnetic field, induced voltage or the tone produced by the pickup. Bobbins are simply there to hold the pole pieces and coil in place. Some still insist on using butyrate for humbuckers believing it will make the pickups sound more authentic, but it doesn’t.
Plastic bobbins for single coils have one major difference to fiberboard bobbins. In plastic bobbins the pole pieces slot into a sleeve joining the top and bottom of the bobbin. This means that there is always going to be a small gap between the coil and the pole pieces. It does have the ability to change the tone of the pickup, but with pickups having so many tone changing variables, but the difference in tone is negligible.
Some pickups have metal baseplates. Humbucker base plates are usually made from either nickel silver or brass. Nickel silver is the preferred choice in most instances, but brass is used in many budget pickups and some more expensive ones. Choice of base plate material will affect the tone if it is made of metal. Any metal within the magnetic field of a pickup will have an influence on that magnetic field, and will itself induce small electrical currents known as eddy currents. Nickel silver is less conducive to eddy currents and is the first choice for that reason. Brass baseplates have a tendency to darken the tone more than nickel silver, but that could be a good reason to use brass if that is the effect you are looking for.
Fender Telecaster pickups often have copper plated steel for baseplates. This also will darken the tone, but the end result sounds good and helps to give the telecaster it’s unique voice.
All pickups were originally designed to have covers. The plastic variety have no impact on the pickup’s tone, but the metal ones do. Nickel silver is the preferred option again for the same reasons. Eddy currents have their part to play again here. Some prefer the tone of a pickup with a cover while others prefer a more open sound and either remove them or buy them with no cover. It’s a matter of personal choice.
Slugs and Adjustable Pole Pieces
Humbuckers use steel slugs in one coil and steel adjustable pole pieces in the other. P90 pickups also use adjustable pole pieces in a similar arrangement. Slugs and adjustable poles are used instead of alnico pole pieces. Pickups of this variety utilize a bar magnet inside the pickup. Due to their proximity to the bar magnet, slugs and pole screws extend the magnetic field out of the top of the pickup in a similar way to alnico pole pieces.
We have covered all the parts for most single coils. Other parts in humbucker pickups include steel keeper bars, baseplate screws, lead wires, and spacers. Any metal parts will have some sort of effect on the tone, and while choosing brass baseplate screws over steel ones might seem wise to some, in reality any difference is indistinguishable. Nonmetal parts can be made of any material, as long as the dimensions don’t change, the tone won’t change. I have even heard one boutique pickup manufacturer suggest that their PAF reproduction pickups achieve authentic vintage PAF tones because they use spacers made with West Michigan Maple. If those spacers were made of cheddar cheese, those pickups would sound the same.
Vintage correct materials and manufacturing techniques are not essential for good tone. Certainly, the use of vintage style cloth insulation on hookup wires doesn’t improve tone but, it’s nice to work with. In addition, there is no justification for claiming that all vintage things were good, and all new things are inferior. The idea that no-one has learned anything in fifty years is foolish. Many of the vintage styled pickups available today are vastly superior to the majority of genuine vintage pickups and they can be expected to be consistent as well. Vintage pickups were mainly characterized by variability and that equals inconsistency in quality. While good and bad tone are subjective judgements, there is no possible argument for claiming that random variations produced consistently good results, and that consistent design and manufacturing produces consistently bad results.
At the end of the day if it sounds good to you, then it is good enough. Some really cheap pickups can sound great but it’s a gamble, medium priced pickups should be expected to sound great no matter what. Premium priced pickups are simply too expensive and don’t sound any better. Spend $10,000 on a genuine pair of 1959 PAF pickups and one thing is certain. You are going to convince yourself they sound amazing to justify the expense even if they don’t, that is until that 60-year-old coil insulation starts to break down of course.