Keeping your stated goal of “a vaccum tube” firmly in mind, go now to the “Wiki documentation” pages on blender.org and read every page through. Even if you do not understand what you are reading (yet), keep reading or skimming.
Don’t attempt to work on your project in earnest until after you have completed this exercise.
No, I am not simply trying to say, “RTFM.” There is a certain foundation of background knowledge which you need to acquire, or at least to have been exposed to, before you can make reasonable and sustained progress toward modeling your tube. Any one of us might be able to do the job fairly quickly, but only because our thinking would stimulate associations with the various things that we have already read. You need to do that reading, too.
Video tutorials, also, are very helpful. Again, you might not understand a tenth of what you are seeing, but your subconscious probably does… more than you realize. The more information you expose yourself to, the more connections will take place “spontaneously.”
I think that your choice of “a vacuum tube” is an excellent one. (Perhaps it should even be a Weekend Challenge.)