To be clear, the OP was asking about the pickup Jeff Beck received vs the "production" JB. To answer his questions more precisely:
- Yes, the production JB uses the same type of wire on each coil.
- Yes, Jeff Beck's original prototype pickup had an A2 in it.
- "Why" were changes made to the original design? You'd have to ask Seymour! There may have been additional characteristics Seymour desired or considerations surrounding the actual production of the pickup (maybe he got a better deal on A5 magnets!).
Edgecrusher, there's no arguing that the material composition of the JB has changed notably since the early days. However, how much these changes audibly affect the end signal is largely debatable, as you said. After all, the core wire type and wind geometry has remained the same.
Personally, I do not subscribe to the idea that the presence of butyrate bobbins and maple spacers contribute to an audible difference that 99.9999% of us could hear in a proper blind test.
Also, does a minute, merely potential variation in coil geometry due to wire theoretically "squeezing" the core of a butyrate bobbin overpower the affects of more prominent variations in wire tolerance, magnet types and pole piece materials? I strongly doubt it. Besides, you'd have to induce quite a bit of tension to start deforming butyrate significantly and the JB uses a much thinner wire (44 gauge) than even PAF types (42 gauge), meaning that it can't resist as much tension and certainly can't do so without stretching undesirably, which poses another issue in regards to consistency.
Like you, I do suspect that the pole piece composition has changed over time. We already know that magnet suppliers changed over time and that the exact composition between magnet lots, even from the same supplier, could vary. I see no reason why this couldn't be true of the hard parts over the years, such as the slugs and screws. Additionally, magnet wire can have a large variance between production lots and, back in the early years, SD didn't have the testing processes in place to insure consistency of the wire like it does now. Yet, despite the process improvements, you still see production "tolerance" being a concern even today.
Wax potting of butyrate vs polycarbonate is also a hotly debated topic...
So, what really separates an "old" JB from a newer one? Is it the species of wood used for the spacer? Is it the density of the pole screws? Is it the longer mounting legs or the unique "life" the pickup has led over the past 35 years?
There's no single factor. But, for all these variables, the JB's sound remains largely unchanged and I think that's what ACE was getting at.
If you want the absolute closest thing to the "old school" JB, the 35th Anniversary is your best bet. If you want to recreate the pickup Jeff Beck received in his Tele-Gib, the Concept JB is the one you need.
