if that often. Even our least reliable tubes were good for a month or two.
When we had to replace tubes, each section was separately powered, so we could shut them down individually. And attempting to replace a tube without removing power from the system either got you a reputation as the electronics tech equivalent to "script kiddie" or a very nice wake at which your former co-workers consumed mass quantities and stood around shaking their heads and saying "What an idjit."
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