I don't recall where i saw this but i know it was many a year ago and it dealt with converting a small light glob into a triode ...from the out side of the bulb ,wrapping a wire around the bulb for the control grid must of been some sort of insulation material around that then tin foil for the anode ,forgotten how the cathode side of it was done .
I suppose you can in that its done with magnetism for CRT deflection with yokes from the outside .