Very much On Topic: Integrated Vacuum Tubes - test-drb@ccmp.vtda.org

21 Apr 2005

...
   I think acorn
tubes are smaller.  Those are UHF tubes -- I   think they 
  were used in 1940s or 1950s vintage equipment for
oscillators or  
    Ummmm - no.  A nuvistor could very nearly fit into the 
 acorn's envelope. 
 Nuvistors look like a largish metal pencil eraser - they're 
 substatially smaller internally than an acorn tube, as well.  
 And of course, as you mention, 30 years later in design. 
Not smaller, but more along the lines of classic (glass, pin sockets)
tubes. Motorola WWII walkie-talkies used "pencil tubes". I've only seen
them once, about the size of a small woman's pinkie finger.