Rails Vs "normal" Humbuckers

The upside of rails: the magnetic field is more uniform along the coil. This is good for bending, as a string's signal doesn't fade due to being bent away from a dedicated polepiece. It also makes matching string spacing to the pups a non-issue, so the pup works well across a variety of guitars, pup positions and non-standard string setups (e.g., 12 strings).

The rails downside: there is no way to perfectly balance all the string signal levels, since there are no individually adjustable pole pieces. Of course, one may still adjust bass side relative to treble, but that's it.

Carvin has tried a hybrid approach by offering a pup with 11 pole pieces, so the magnetic field is more continuous between strings, yet still individually adjustable. Nevertheless, I have yet to hear anyone rave about the tone of Carvin guitar pups.

I'm not sure the rail design itself really affects the tone any more than the usual factors -- magnet type and strength, number of windings, coil wire, shielding, distance to string, basic geometry of windings and field => pup sampling aperture. However, rails seem to be associated with more aggressive, modern pups -- I would be willing to bet it's more of a marketing decision, as those who buy "vintage" type pups would not be likely to go for a vintage sound with modern appearance.

Thanks for the answer Gnease! I definitely learned something today :D

I suspect that it was partly also a way to get a humbucker into a single coil size.

I think it was, like was said, an attempt to get a dual coil humbucking pickup to fit into a single coil guitar without modifying the guitar's appearance too much. A good thing if you have a collectable guitar but play around a lot of noisy stage lights.

And the rail or bar I think was a good way to get a smoother, more continuous magnetic field as the strings are bent.

I think I also saw a normal size dual coil Bill Lawrence pickup that had rails instead of adjustable pole pieces at one point. Same idea, regular size.

Thing is, people nowadays don't seem to experiment with adjusting the adjustable pole pieces, lol. A pickup sounds too muddy or bassy, and they just change the pickup instead of lowering it and bringing the pole pieces up. And the opposite it true too - too trebly and they quickly ask which pup has more 'balls' and grind. There's a lot that can be done with adjusting heights.

When I was looking for a humbucker to fit my Strat, I saw some company's rail type pup and thought it would somehow have too wide a spread to maintain the 'focus' of the single coil. Not lengthwise, but in width. I saw the pole pieces of the single coil right in the middle of the pup and then thought the two rails would somehow be in 'the wrong place' under the string. A small consideration to be sure, but having come from a time when tweaking pole pieces was more or less the norm, I was aware how much difference height adjustment coule be; having two separate metal pole strips near the edges of the pup made me think the sound would not be under the correct harmonic.

Then I saw the Duncan Hot Stacks, and at least to me, that made the best sense - the pole-bars being right where the original pole pieces were. Good, loud (hence the 'hot' in Hot Stack) humbucking signal. That's what I was after at the time, being in various venues with questionable power and lighting.

I think Carvin did have a good idea with the eleven pieces too! But then again, most people don't spend the time to adjust them. :)

I suspect that it was partly also a way to get a humbucker into a single coil size.

A good point, though rails do come in all forms: single coil, full sized 'bucker, single sized 'bucker.

Thing is, people nowadays don't seem to experiment with adjusting the adjustable pole pieces, lol.
Okay, that's probably a real newbie question but I'll ask anyway... How does one adjust the pole pieces? By just pushing on them until the sound is right? Wouldn't that risk damaging the coating on the coil (assuming that the pole piece is in contact with the coil itself). Also, Humbuckers have two rows of pole pieces, are they adjustable the same way?

Adjustable polespieces are threaded to screw in and out, and have either an obvious slot or a hex socket to accept a standard screwdriver or allen wrench. On most humbuckers (including the SD in your image) only one set of polepieces is adjustable -- the other is fixed, so don't try to move those. There are exceptions; the 'bucker on my Burns guitar has two adjustable rows of polepieces, but it's probably just for cosmetics (ironic, given the guitar).

An exception is the Strat pup. The polepieces are actually individual magnets that may -- with EXTREME CAUTION -- be pressed in or out. However, this may very well damage the pup, and if the polepiece loosens, must be reset with some sort of adhesive/glue. This is an operation only for the technically savvy and/or well-moneyed.

A good point, though rails do come in all forms: single coil, full sized 'bucker, single sized 'bucker.

So do "normal" pups, but it doesn't change the fact that the first pups were single coils. What were the first rail pups? :?:

A good point, though rails do come in all forms: single coil, full sized 'bucker, single sized 'bucker.

So do "normal" pups, but it doesn't change the fact that the first pups were single coils. What were the first rail pups? :?:

Memory says Bill Lawrence single coil blades -- but I could be wrong.