"MUSICAL COMPONENTS."

New Zealand Herald, Volume LXVIII, Issue 20986, 24 September 1931, Page 15

"MUSICAL COMPONENTS."

HUMMING OF TRANSFORMERS.

NEED OF TIGHT LAMINATIONS

Headers from time to time report what may bo called the "musical transformer" —or as a variant it may bo a musical choke or similar component, fn such a case the sound comes from somewhere inside the set, even when the loud-speaker is disconnected, states Popular Wireless. I his seems to be very puzzling to many people, but really it is perfectly simple, and the action is precisely similar to that of the loud-speaker itself. With a loudspeaker you have the speech currents actuating the electro-magnetic system and producing vibrations of a diaphragm. In a transformer, for instance, you have the same speech currents traversing the windings and therefore operating electromagnetically on the laminations of the core. For the highest efficiency in the transformer these laminations should be rigidly clamped together, as any movement of the laminations involves the dissipation of some of the energy in the windings and means overall losses. But quite often the laminations arc not really tight and one or more of them will start vibrating in accordance with the speech currents in the windings. This, therefore, acts in exactly tho same way as the armature of the loud-speaker, and if you put your ear closo to the instrument you may bo able to hear tho programme definitely coming through. But there is nothing at all mysterious about it, and the only practical comment to make is that the transformer should be tightened so that the effect is eliminated. Probably the most familiar case is the humming of a transformer when connected to the A.C. mains. It is almost impossible to prevent a transformer fiom humming ; some are fairly silent, but you can almost invariably hear the hum if you listen very closely. Here, however, the strength of the currents is enormously greater than in the case of a speech transformer and the difficulty of keeping the laminations stationary is correspondingly increased. If the effect is pronounced (whether in a mains transformer or a speech transformer) it certainly calls for attention, because a vibrating lamination may quite possibly cause damage to a wire which happens to come in contact with it. It is true that the windings of the transformer should be completely protected from the core, but sometimes the leading-out wires may lie in close contact with the core at some point or other.

HIGH-VACUUM VALVES. DISPUTE OVER INVENTION. DE FOREST AND LANGMUIR. There has been a pood deal of dispute between the De Forest interests and the General Electric Company of America in regard to the so-called "gassy" valve originally used by De Forest and the high-vacuum valve later brought forward by Langmuir, states an English journal. The Langmuir patent was granted in 1925 and has passed by gradual stages through the several Courts, finally reaching the Supreme Court. In view of the very high value placed on the patent by the American General Electric Company, the fight for its validity has been a very energetic one. The basis of the Langmuir patent is the production of a valve for radio purposes from which all traces of gas have_ been removed to the highest degree attainable by known modern methods. Valves in which a trace of gas is allowed to remain are classified as "gassy" or "soft" and, are apt to become unstable in use, and are limited in their ability to control higher currents. Although l)e Forest in 1908 obtained a patent on a three-electrode valve fairly highly evacuated, the American General Electric Company claim that the researches of Dr. langmuir during the years from 1913, when the first application was filed, to 1925, when the patent was issued, had perfected the design of the valve to such a pitch that it was not to be considered merely as a question of degree, but the. valve was to bo regarded as being entirely different in kind. . To what extent De Forest realised that the difficulties and uncertainties of the "soft" valve could bo got over by concentrating upon an extremely high degree of vacuum is a matter which the American Courts no doubt had to consider very carefullv. Apparently they have decided'that the development from a- so t valve to a "hard" one is merely a matter of degree, while the Langmuir attorneys naturally contended that ! fc°from "hard" valve was utterly different from the "soft" v;,lvo in its nalure • n constituted u, totally new step in invention. NOTES AND COMMENTS. The presentation of "'lho Arcadians by the Hamilton Amateur Operatic Society on October 7, will be relayed by IYA On October 9 the story o the ••Marie Celeste" will be recounted by "Leo Fore Brace." A pleasing feature at the ]f ,\ icn ' s sos.sion, conducted by "Uncle Reg dt IV \ yesterday, was a recital by the cho.i from 'the. Mcadowbank school. A numL of the. children sang the original themes, while others rendered the descanls. The programme proved very enjo)a hie. Conditions were unfavourable on luesday morning for a rcbroadcast by 1 > the London Faraday Centenary celebrations. The station was om the air and rendered a programme of British numbers. ■\ Rome station was-picked up at goorl strength, but after a few minutes signed off. The International Broadcasting Union includes almost all European broadcasting organisations except Russia and a few small countries and represents about 12 500 000 licensed listeners. Vice-Admiral Carneiidale, of tile has been reelected president for 1931-32 and Messrs. Giesecke, Germany, and Tabouis, trance, vice-presidents. Tlio union has resolved to organise a series of European concerts, to bo given in turn by the different member countries and relayed, as far as possible l.iv all members The union also hopes to fcecure from tlio 1932 Madiicj International Convention, an extension of the bands of frequencies allocated to broadcasting.