It tests vacuum tubes that would usually come from televisions. If a tube was bad you could hypothetically replace the tube and get your TV working again. The various holes are for the various tubes that were sold.
Vacuum tubes would eventually be replaced with transistor designs as transistors were more reliable and required way less power to operate. Also they were vastly smaller than tubes. Today most TVs are, in essence, a small computer packed into a single chip called a System on a Chip (SoC), so they are way less user repairable. But they're also vastly cheaper than the 1930s versions. In 1939 RCA's TV that they sold went for ~$600 or about $13,280 in today's money.
So there was a ton of incentive to make TVs as user repairable as possible. It's also why we used to have a lot of TV repair shops that we pretty much have zero of today. Putting that much investment into something, you'd want to make it run for as long as possible.
spongebue@lemmy.world 11 months ago
Love your description, but I would add that radios were arguably an even more common reason for people to replace tubes. Also, while television stations did exist as far back as the late 1920s it really wasn’t until after WWII that it became semi-common for the middle class - I live in Denver and we didn’t get our first station until 1952, for example.