Re: Covered humbuckers
It's an interesting question Blueguitar, and one which may not have a definative answer. I have book called "50 Years Of The Gibson Les Paul", and there is a small section about Seth Lovers humbucker design that mentions the covers. Here is what it says:
"Additional screening for Gibson's original humbucking pickup was provided by a metal cover, as Lover explained. 'The cover helps shield away electrostatic noises from flourescent lamps and so forth,' he said. 'I needed a material with high resistance so it wouldn't affect the high frequency response, and I considered non-magnetic stainless steel. But you can't solder to it. German silver has high resistance, and you could solder to it, so I used that.' "
I can certainly see it acting as a shield, but with wax potting today I wonder what real difference even that makes anymore? I think the point that you can move the pup a little closer to the strings without the cover is valid, and that may allow for certain frequencies to be accentuated. It's a lot of fun playing around with the small differences for sure.
Cheers.