Someone with more electronics knowledge than me can school me, perhaps--
It's interesting to me to read that people find that shielding control cavities helps with hum in single coil pickup systems. For high frequency interference, this makes sense to me.
But I've never personally found it to help with radiated 60 Hz hum, and can't understand the mechanism behind how a foil shield (as opposed to a high-permeability shield like Mu-metal) could have a significant benefit at hum frequencies, particularly when the pickup coils themselves are mostly not going to be shielded. What am I missing?
Thanks in advance!
You are correct, shielding the control cavity isn't going to stop the primary source of hum, which is the enormous coils of wire specifically designed to be sensitive to electromagnetic interference aka "the pickups".
RF noise can be reduced by shielding, and in Fender guitars where the wires themselves are not shielded this *may* help...
The Jazzmaster I owned had a soldered, solid brass shield in the entire rout, it was no less hummy than any other Fender, certainly..
Guitars are fairly high impedance environments, so they are susceptible to interference. I noticed that in cold, dry weather, brushing my hand on the pickguard of my Telecaster produced a lot of static, it sounds like a Geiger counter..! If I were to coat the bottom surface of the pickguard with a conductive material this would dissipate the static charge and reduce that noise.
Lower resistance pots would help too.. (this one has the 1966 1MΩ tone and volume pots).