In my grandmother's house a huge Stromberg-Carlson radio stood against the the living room wall. It was the size of a church window. The whole family could gather around it in the evening listening to Kate Smith or Amos 'n' Andy. The radio was big because the electronic tubes inside were big. The size of Coke bottles. And glowing red hot.
By the time my parents got their own house electronic tubes had shrunk to the size of salt shakers. The radio sat on a table, not on the floor. Every weekday afternoon I sat beside that sturdy Zenith listening to Tom Mix and Sky King.
On my 14th birthday, in 1950, I was given a radio of my own, a little Sears Silvertone, about the size of a recipe box. Inside were a half-dozen tubes the size of lipsticks. Tubes were shrinking fast, but they still glowed red hot, so they needed space inside the box to keep them from overheating.
Then along came transistors, the size of pinheads, that did the same thing as electronic tubes, but more cheaply and reliably. Didn't burn out. Didn't break. No more trips to the tube tester at the drugstore with a paper sack full of tubes. Because transistors worked at room temperature, lots of them could be packed close together. Radios became the size of a pack of cards.
And that's where things stand. I recently bought my wife a little Grundig radio, also the size of a pack of cards. But the new radio gets AM, FM, and world band short-wave. The size is limited by speaker, speaker power, aerial, knobs, dial, battery. Today, the electronic circuitry for thousand radios could be packed onto the period at the end of this sentence. It's been a hellava ride.