REVOLUTION IN VALVES

Manawatu Times, Volume LIV, Issue 6802, 4 January 1929, Page 10

REVOLUTION IN VALVES

ADVANTAGEOUS TO BROADCAST RECEPTION. Something radically new and advantageous to broadcast reception has not excited the radio world for a long time and some of the more experienced listeners have been inclined to believe that radio science was flagging. The recent advent of what is commonly known as the “screen-grid” valve, however, marks a big step forward in technical development (says an exchange). ’This valve has come to us first from America, and under proper conditions laid down by the manufacturers it has-proved a veritable wonder as a radio frequency ampliiier, not only on the ordinary broadcast band of wavelengths which have proved so effectivo in bringing., concerts., to New.. cZalaud.. from., the., furthest side of tho globe. The short wavelength signals have always been difficult to amplify before they enter the detector valve, and the standard practice has been to amplify the signals only after they have been detected. The new “screen-grid” valve now makes it practicable to employ radiofrequency amplification on the short wave-lengths with extraordinary success. The new valve' has a proved efficiency equal to three ordinary valves, provided that it is shielded strictly in accordance with the manufacturers’ instructions. The method of shielding offers no difficulties, and those who arc operating the new valve are loud irt its praises. It has a voltage amplification factor of 00, as compared with that of the 201 A type vaivc, which is 54. The American “screencd-grid” valve employs a filament voltage of 53 volts. An English “screcnod-grid” valve will also almost immediately be on tho New Zealand market, for which great things a.re claimed. It operates with 6 volts on the filament, and is somewhat- different, iu design from the American type, though similar in principal. Both American and English “scrcened-grid” valves arc for use in the ordinary broadcasting receiving sets as well as short-wave sets, but certain modifications in the wiring of all sets are necessary to adapt them to the new valve. Above all tho valves must be properly shielded in metal compartments.