I'm quite interested in home-made devices, last year I tried making a sinusoidal wave oscillator at home and succeeded. It feels good to DIY some coarse devices, and recently I'm learning to build a Cathode Ray Tube. However, it's not going successful with me; I would like to build an electron gun first, but the "emission mechanism" confuses me most. From wikipedia, http://en.wikipedia.org/wiki/Electron_gun, it's said that there're 4 ways to emit electrons: thermionic, photocathode, cold emission, plasmas source. I want to avoid using high voltage source (not higher than 220V AC) at home, can anyone give me an advice ? By the way, what I think of electron emission at the very beginning is a "metallic board" and an "electric field" that drives the electrons out of the board. If I want to do it in this way (maybe very unrealistic), how strong should the "electric field" shall I apply on the surface of the board to drive the electrons out of the metal (e.g. silver, copper, iron, cobalt, zinc)?