Page:Popular Mechanics 1928 01.pdf/137

 



The tube shown in the photo is one of the few really new developments in the radio field for some time. Designed to give much greater amplification in the r.f. stages, this newcomer, announced by Mr. Elmer E. Bucher, of the Radio Corporation of America, is to be known as the UX-222. The tendency to oscillate just short of the point where maximum signal strength is attained has been the outstanding fault of the standard tube. While oscillation is very desirable and necessary in generating the broadcast carrier wave, its presence in the receiver amplifying circuit renders the standard tube useless as an amplifier until oscillation is suppressed. The voltage-amplification factor of the new tube, due to its unusual construction and methods of application, is said to be from 30 to 150 without a squeal; the average r.f. amplifier gives an amplification of 6. The B-voltage is 135 maximum, the filament voltage is 3.3, just .3 volt more than that required for the 199-type tube, and the amperage needed is .13. The new tube is at present designed for battery operation only. Its use is limited to the improvement of amplification in the r.f. stages, and it is not adaptable to present-day sets. Each stage of r.f. must be thoroughly shielded, as shown in the circuit diagram, and three tubes should be used to obtain maximum results. The tube has two grids in addition to the usual filament and plate, the extra grid being said to make the circuit more stable by preventing feedback. No neutralizing methods are required in the receiving circuit when the four-element tube is employed. Hence, the construction is simplified and the set is more easily controlled without the customary howls and squeals. The point on which the greatest interest is focused is the amplification factor, which is 30 to 50 