UNITED KINGDOM - JULY 13: For its time, the Marconiphone P17B was a very compact, ingeniously designed battery-powered four-valve portable radio. It had four valves, was battery-powered, and could receive medium and long wave broadcasts. The receiver switched on automatically when the lid, which contains the aerial, was opened. The drawback with portable valve radios was their high power demand on the batteries, which made them expensive to use. Following the invention of the transistor in 1948 by William Shockley (1910-1989), transistors began to replace thermionic valves in radio receivers, allowing much smaller, more affordable portable radios to be produced. (Photo by SSPL/Getty Images)
