When I asked this question of the Engineer, his answer was that, yes, all of it was turned-on, all the time, twenty-four hours of every day, and that they kept it that way for reasons of both security and economy: Security, because if any piece of equipment were ever to fail, the station would always have another of the same thing, already warmed-up to replace it, and would never have to risk going off the air. Economy, because, even despite the electricity cost (remember that this was in the early '60s and electricity was very cheap), all of those tubes would last MANY times longer, saving on both the cost of the tubes and the labor to replace them. He went on to explain that the thing that causes tubes to "wear out" is not their operation, but the repeated heating and cooling cycles that come from turning equipment on and off again whenever it is used. This, he said, eventually results in a form of "fatigue" to the metal elements of the tubes and finally results in their failure. Just as a light bulb will last much longer if you just turn it on and LEAVE it on, he said, so will an electron tube.