VEST POCKET RADIO

New Zealand Listener, Volume 15, Issue 382, 18 October 1946, Page 21

VEST POCKET RADIO

America of a tiny radio valve weighing less than a tenth of an ounce and occupying only a little more space than half a cigarette has made possible the pocket radio set of which photographs appear on this page. The set, including batteries, stands six and a-quarter inches high, is three inches wide and three-quarters of an inch thick, and its to‘al weight is 10 ounces. Its earphones lead is also its antenna. ; The development of what are called "sub-miniature" valves (or "tubes" among technicians and Americans) made possible the proximity fuses used in the recent war (particularly in anti-aircraft shells), and in peacetime will be applied ‘Tie post-war development in

to hearing aids-and pocket radios. The pocket radio shown here has five plug-in tubes, which weigh about half an ounce altogether; they perform all the functions of normal size tubes used on ordinary superheterodyne radios. Since two of them are actually combingtions of two tubes in one, the set is equivalent to a sevenvalve radio, and an NZBS engineer says that such a radio would not be restricted in range, except by the smallness of its aerial. The elements inside the valves-the filaments, grids and plates-are all located and held together at top and bottom by very thin pieces of mica which have previously been punched very accurately with locating holes. All the metal parts are held together by welding. The filament is of wire less than a 1/1,000th of an inch thick, made. by being drawn through fine diamond dies. These valves contain more parts than the ones used in proximity fuses or

hearing aids. About 30 separate parts go to make up one of these, and the assembly is done by automatic machinery. Of the five used in the pocket radio shown here, two are known to radio engineers as radio frequency amplifier pentodes; one is a triode-heptode frequency converter, one a diode-pentode detector amplifier, ana the fifth is an output pentode similar to the kind used in hearing aids. To operate all five requires less than a third of a watt, and takes a miniature B battery of only 22% volts. The batteries would probably run up to nine or ten hours before they would have to be replaced. People who have to equip themselves with hearing aids will no doubt be interested to see how the price of this luxury radio compares with their necessity article.