Radio News Sylvania Ad, February, 1947

This colorful back-cover Sylvania advertisement trumpets the virtues of "lock-in" (also known as "loktal") tube sockets. This type of socket was suitable for wartime applications, where lots of jolting and vibration was to be expected. Sylvania's lock-in ads ran throughout that year. Another ad from September, 1947 is typical of the series.

The loktal design was popular for a few years following World War II, but was quickly superseded by all-glass "miniature" tubes, which were smaller, lighter, and cheaper to make.

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