Before, during, and after the advent of the transistor radio, there lived a short-lived creature known as the subminiature tube radio. It was sort of a commercial after-effect of vacuum tube technology developed during World War II for Allied Forces radar equipment. About the size of a cigarette butt, a subminiature tube was MUCH smaller than a standard vacuum tube, or even a "mini tube," and therefore it used much less power and generated much less heat. This meant that Allied radar units could work faster and more reliably, and that meant a higher return in dead Axis soldiers.
Postwar benefits proved less concrete. In 1955, as the first transistor radios began to be produced and marketed, transistor devices themselves were still so expensive to produce that, for instance, Raytheon's transistor sets employed only transistors which had been rejected for use in Raytheon's military contracts. The 10-year-old technology of subminiature tubes became a convenient stopgap measure for a number of radio manufacturers who wished to compete in the new venue of pocket radios.
In those early years of transistor device development, getting a transistor to process a (low frequency) audio signal was many times easier than processing a (high frequency) radio signal, and therefore many times cheaper. And in the marketplace, this translated into "Hybrid" tube/transistor radios which employed, usually, a pair of transistors in the radio's audio circuit and three subminiature tube for the RF circuit, and the word, "Transistor" proudly stamped on the radio's cabinet face. The Automatic Tomb Thumb 528 is an example of a subminiature tube radio, and the TT-600 is an example of a hybrid 3-tube/2-transistor radio which identifies itself simply as a transistor radio...
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