Ad for a tube tester. These were found in drug stores, grocery stores, and other venues. You would rock up with some tubes, and plug them into the right socket on top. Then the tester would tell you if the tube was good or bad. If bad, it had drawers full of new ones, which you could purchase to replace your bad tube.
When transistors took over, there was no longer a need for tube testers, and they faded away by the beginning of the 1970s.
Here is an RCA branded one in the flesh.
There were multiple sizes of tubes, so the unit had to have a bunch of different sockets on top to accommodate anything someone might have. That forced the top of the unit to be the size it was, to fit all those sockets. Then, the pedestal held the replacement tubes, so that also had to be big enough for drawers full of boxes.
It was common to bring in multiple tubes to test, since you wouldn't know which of the tubes in your TV or high-fi set was the bad one. You'd test several, and buy a replacement for the bad one.