Not the easiest DIY project but this homemade Homemade Oscilloscope looks and works great.
“Homemade Cathode Ray Tube with cold cathode. Vacuum is somewhere between 100 – 200 microns, easily attainable with amateur equipment. Vertical deflection is done using an electrostatic plate. This CRT is used as an oscilloscope to display a signal from a sound synthesizer. “