I generally do that kind of work in spaces that are non-carpeted, dressed lightly, and as much as possible on wood tables. Also, once you get into the case, figure out where the ground plane is on one of the boards and find a good spot on that to use to ground yourself on a regular basis. (It's usually the largest trace on the board, as it needs to be accessible basically everywhere.) Glad you had no problems!
This, except with tube power amplifiers. Also, they need to be plugged in and running so the tubes are nice and hot (and the capacitors are all charged).
Jokes aside, pretty much all modern electronics have enough ESD protection built into them that you don't really have to worry about it unless you're actively trying to damage something.
Would it be right to say that ground planes are blank spaces on the motherboard?
A lot of times they are - you can usually follow a trace from that region back to a connection to one of the wires from the power supply, and that's a good way to confirm.
