Some of the early glass tubes used in transmitters were truly works of the glassblower's art.
When I worked at Fermilab, the RF Power Amplifiers used in the Booster and Main Accelerators used water-cooled metal-ceramic tubes made by Eimac.
They were 4CW100000X, indicating they had a Plate Dissipation of 100,000 Watts!
A quick look at the "Eimac" website doesn't show them listed anymore, so I'll have to get a hold of my buddy Dave who still works there and find out what they're using these days.
Anyway....a friend of mine sent me the link to this AT&T video about the Good Old Days.