[Speedslug]

I did a little looking at this some 10 years back and found a video that said the leads through the glass needed to be a particular kind of metal because the expansion of the glass when heated (COE = coefficient of expansion) is different than the expansion of the metal.

Since the two materials don't expand at the same rate they also don't contract at the same rate so it's hard to get a seal tight enough to hold a vacuum.

Then there is the issue of drawing a vacuum on the "tube" while closing the tube.

You could try running the leads through the mason jar lid with the screw ring loose while it is all inside one of the large vacuum jars that come with the food sealer with a good length of wire connected to the leads set inside the vacuum jar while you draw the vacuum down.

You would want extra length of wire so that there wouldn't be any possibility of heating the sealed through access on the mason jar lid.
Once a vacuum is established the lid to jar contact point will hold the vacuum inside until you get the whole out of the containing jar and screw the ring on tight.

It's likely to all be an exercise in frustration this way as I don't see a way to pass leads through the lid in a way that will seal let alone not short out the signal lines.

Keep looking for " making vacuum tubes " videos. I forget where I found it.