Simply said it destroys electronics. After an EMP there will be no working radio, television, telephone, power-grid, car or cash-machine.
Banks will stop working and even a millionaire will not be able to buy any food.
People who need medicine or care will have to try without.
Although vacuum tubes are far more resistant to EMP than solid state devices, other components in vacuum tube circuitry can be damaged by EMP.
Protecting against an EMP can be done with the help of a cage of Faraday.
Put your vacuum tube transceiver in a metal box. Make sure the equipment does not touch the metal cage/box. Don't ground the cage/box.
To operate your now state of the art station after nuclear disaster strikes you need power. Remember the power-grid is pre nuclear history and you need your own generator and battery to get up on the air.
More info here:
http://www.peakprosperity.com/wsidblog/87871/building-your-own-faraday-cage
