Classic Vacuum Tubes
X-ray image depicting classic vacuum (electron) tubes. Left to right: a 1932 RCA 83; a 1936 National 47; and a 1950 Sylvania 6BL7GT. In the early twentieth century, vacuum tubes allowed the development of long-distance telephone service, radar sets, radio broadcasting, television, and the first electronic digital computers. After the 1950s, vacuum tubes were replaced by transistors in virtually all applications. Image taken with an X-ray system (ZEISS Xradia Context).
—Herminso Villarraga-Gómez, Carl Zeiss Industrial Metrology, Wixom, MI, USA