William Donzelli wrote:
  Any triode will work in a digital fashion. 
Umm not really ... read the fine print that comes with your triode.
The reverse is often true -- digital tubes make great audio tubes.
  See 5965 for a typical computer tube.
    But yes, we
need the OP to give us a few more guidelines as to where the
  boundaries are, as "1900-era materials and modern knowledge" covers way too
  much ground. 
 Modern knowledge of computer architecture only, perhaps. 
 
Digital is the modern idea.
  --
 Will
 .