Are home-built devices allowed to be made using things like pre-manufactured valves and transistors? What about integrated circuits? Where's the line drawn?

Are home-built devices allowed to be made using things like pre-manufactured valves and transistors? What about integrated circuits? Where's the line drawn? Am I allowed to order some parts from Digikey and assemble them into a widget, or must I start closer to the beginning by mining my own ores?