I used E-wire to make up the glowing cathode element. I am sure that different colours, patterns, or alpha numeric characters could be used in the display.
I managed to fool my father, from a couple of feet, that it was a real vacuum tube. He had worked with tubes when he was a young man, and at first sight was shocked by the size of it.
The final tube is about 13 inches or 32cm (see D cell battery in picture for scale)
1 Glass dome (I think this came from a clock, and was Thrift store find at one dollar)
2 ABS Plumbing pipe coupler (four dollars at a hardware store)
3 Luminescent wire, EL wire , ( I bought this at Ikea for a few dollars)
4 Scraped computer hard drive and mounting rails (Free!)
5 Scrapped computer parts ( I used the screws, drive rails, stand offs and other scrapped bits, all free)
6 Black Arborite, or black painted, wood half an inch or 1.5 cm thick (Ikea for three dollars)
7 Large nails ( I used nine, six inch nails and cut the pointed ends off)
Things to consider:
Make sure you have your glass dome with you when you buy your pipe or pipe coupling.
You want a snug fit. I had to sand out the inside of the pipe to get the glass to just fit.
I wanted to be able to remove the dome, but you could glue it if you need to.