EMP weapons get a lot of hype these days, but it’s mostly Hollywood hype. The real weapons don’t live up to their reputation.
There are two main problems with EMP weapons. The first is that it’s very difficult to generate a powerful EMP. You pretty much need a nuke to make an effective EMP weapon. Without a nuke, you are limited to teeny tiny EMP weapons that are only effective over a very small range.
The second problem is the inverse square law. Your EMP drops off at a rate equal to the square of the distance. In other words, at 2 feet away it has 1/4th the power it had at 1 foot away, at 3 feet it’s 1/9th, at 4 feet it is 1/16th, etc. Because the power level drops off so quickly, EMP weapons, even with a nuke, don’t have a huge area of effect.
One consequence of this is possibly a fatal flaw in your plan. You are thinking that electronic devices will be valuable because of scarcity after the big EMP attack. Even with a massive EMP attack all over the world, you are going to have so many devices in areas that aren’t affected that your electronic devices aren’t going to really be all that rare or valuable.
That said, you may still want to protect your own devices from EMP just because they are your own devices.
As you suspected, you need a Faraday cage. Any completely enclosed conductive metal box will act as a Faraday cage. You may need to check something like a fire safe or other types of metal boxes (like a tool box) because sometimes holes for things like the lock will let certain frequencies in.
You need to take special precautions for any cables and such that might go in and out of your Faraday cage as well. If you have some electronic device that you are trying to keep powered up, just drilling a hole in the side of your Faraday cage and shoving the power cable through there is just asking for trouble.
You might want to move into some sort of steel frame building too. Steel frame buildings with metal roofs make excellent natural Faraday cages. They will shelter you from much of the EMP even if the building has windows and such in it. If you know of some building that is really annoying because your cell phone never works inside of it, that’s perfect.
I poked around on the net and didn’t find anything that I would call a good article on Faraday cages, unfortunately. The concept is pretty simple, though. The energy is going to flow around the surface of the box, leaving everything inside unharmed. Basically, a Faraday cage keeps everything from outside from getting in. It also works to keep anything inside the box from getting out. Your computer case, for example, is required to act like a Faraday cage of sorts, so that radio waves generated by your computer (caused by things like sharp square waves on clock signals on your motherboard) don’t radiate out and cause interference to other stuff in your home.
Vacuum tubes work with higher voltages internally, so if you zap one with some high voltages across its conductive materials it won’t be damaged anywhere near as easily as something like a silicon transistor. However, vacuum tubes are not completely immune to EMP. Zap a vacuum tube with a big enough EMP and you will fry it.
Vacuum tube devices are getting pretty rare these days. Unfortunately, this also means that the audio whackos who think that vacuum tubes make the sound better are going to be the only folks with a working stereo system after the big EMP blast.