Question about valves running hours

Another pertinent question: If valves were the power support to all communications in a recent past (from tv and radio broadcast to military coms), for how long would they live? Would a valve survive more than a few hundred hours? Were they replaced many times a year? Or did the equipments have different banks of valves to switch between them? I'm curious about how people used to operate the tubes 50 years ago.

migueca- I don't know about military/industrial practice, but back in the '60s, it was pretty common for tubes (and free standing tube testing machines that looked like ATMs in size) to be everywhere- drug stores, hardware stores, electronic specialty stores (like Radio Shack and Lafayette) and other places. It wasn't uncommon for a civilian appliance owner to take a set of tubes to such a shop, 'test' them, and buy replacements.  (Sometimes, the new tubes were on shelves behind a door at the front of the testing machine).
If it was a big TV/console and the owner was not equipped to do this, there was a business-- the TV/radio repairman, for lack of a better term- who would show up at your house and do the work. People generally weren't fawning over Telefunkens with specific markings; GE was a pretty common brand at least in the NE States and for these purposes, a tube was a tube, there were 'equivalents' that you could look up (still available as pages on the 'Net) and it all seemed pretty matter of fact. By the mid-'60s, I guess, transistor stuff became more commonplace, but the tube regime hung on well into the '70s or later as a fairly common artifact. (I'm not talking about audiophile or specialty applications, just garden variety tube usage, availability and replacement). 

Whart -  thank you for that "History class" :) It's really interesting to learn how people dealt with gear in the past - this case, valves.
It seems a valve was something simple and common, like a light bulb.

My pleasure. Obviously, that was the States. Other countries, practices varied, I would assume. (Hey, in London they still have a store for barrister wigs and a store devoted to umbrellas if I recall). I'm also pretty confident that the big tube Vlad Lamm uses in his SET amps was long used by the Soviet Union as part of the guidance system for their ICBM (nuclear missiles). It's a pretty robust tube! 

The heat is develop when the power tube plate dissipates,the more watts the more heat and the more heat the  shorter the tube life.A well designed amp should have about 60-70% of total plate dissipation