Faux electronics I'm building...
The metal deposit you mention, Bojan, that's the silvered tops in those tube?
I guess I can use the tubes the way I want without needing to cut/drill into them. If this preserves the quality of the internal structures, then I need to work with this. I'll be illuminating the tube valves with an LED from below. I am guessing now that a stemmed tube (a tube with a bakelite base) might be a better option.
While I'm here, that big central lug that I see in some of these tubes, is it a metal lug? If it is bakelite I can drill into it (with care).