I came across this excellent detailed video, describing how thermionic valves were made. Well worth a look – for example, at Mullard tungsten ore was bought in and converted to metal and then to wire on-site.
Read full article: How thermionic valves were made
from Electronics Weekly https://www.electronicsweekly.com/blogs/engineer-in-wonderland/thermionic-valves-made-2017-04/
Electricals Warehouse 