When I was young, my dad would take the back off the TV, which was a bit dangerous due to the serious capacitance, and take out several tubes. We'd take the tubes to the store, where they had a test machine. It looked a bit like a video game console. Dad would plug in the various tubes, the machine would indicate which was bad, we'd buy a new one, take them all home, dad would plug them all back in, and, et voilà, working TV again.