TIPS AND JOTTINGS

Radio Record, Volume I, Issue 35, 16 March 1928, Page 11

TIPS AND JOTTINGS

| THE object of the "glow tube" regulator for B eliminators is to maintain the correct nominal voltage output at each terminal. ‘This is accompanied by the tube taking a certain amount of current, and when more output is demanded, the tube automatically takes less surplus, thus compeusating for the | micreased demand. YANKEE FILAMENTS REVISED. ‘THE following yalves, CX312A CX871A, UX11IZA, UXI7IA, are now produced with filaments requiring only one-quarter ampere, half the original filament current. ‘There is also a whisper of 201A type tubes to be produced with a filament requiring but one-eighth | amp., halt the present consumption, THE MONITOR’S LOUDSPEAKER. THE fidelity of reproduction of a broadcast depends yery much on the loudspeaker used for monitoring Ti the loudspeaker at the station is "drummy" or "down? in high frequencies, the operators may tend to overemphasise this portion of the- band in microphone placing, equalisation of lines, etc. If, on the contrary, the station loudspeaker is "tinny," or relatively lackmg in low notes, there may be a preponderance of bass in the station’s output withont the oper: ators being aware of the fact. While such effects may benefit some listeners whose receiving apparatus requires acoustic correction, it will result in distorted reproduction in both the good receivers and those which have the opposite fault relative to the monitoring circuits at the transmitter. Thus the characteristics of the station loudspeakers are often an important element in the fidelity of reproduction attained. SHIELDED-GRID VALVES, HE first shipment of the new Americail screen-grid tubes to arrive in Wellington sold "like hot cakes" at £2 each. These tubes appeal to the "hams" as short-wave R.F. amplifiers, and will in many cases also be adapted to the R.I’. stages of broadcast receiv ers. Tubes available in the United States differ considerably from those used in England, uot on account of their electrical characteristics, but rather due to the mechanical atrangement which, in English tubes, seems to have heen worked out with more thought toward ease of use. Captain H. J Round has published a helpful book, "The Shielded Four-electrode Valve," published in London at Qs. 6d. | | B ELIMINATOR REGULATION. THE BEST LOUDSPEAKER? J) ISCUSSING Joudspeakers, the current number of ‘‘Radio News" says, ‘The best combination, however, comiprises a horn and a cone connected to the set, either in parallel or series, and placed is different parts of the room. This gives the greatest fidelity in reproduction available to-day. There are of course, such exceptions as the large exponential horn, which gives very excellent reproduction on both the low and high notes. ‘This speaker, however, tskes up a great deal of room." BATTERY SETS WILL LIVE. THE advent of the a.c. operated set will not mean the death of the battery set, which is bound to continue in use for many years, at least in places where no power supply is available, or where it is unsuitable. At the prescnt moment battery operation is quieter than a.c. yalve operation, although the noises emanating from power lines are practically of no consequence to the average user. It is quite possible that the deyelopment of new valves might even Cause a return to battery-operated sets, owing toa much reduced current consumption. A DEFINITION OF TERMS, AN "electric radio" receiver is an a.c. | receiver containing no batteries or iquids, and works entirely from lightsocket power. An "electrified" set is an ordinary battery-operated set wherein the A and B batteries are replaced by eliminators necessitating no alterations to the set itself, Automatic trickle-charging also comes under the "electrified" heading. GRAMOPHONE PROGRESS, L ECENT advances in the technique of recording and reproduction ‘have reduced the loss in musical fidelity of the gramophone as against direct presentation to an almost negligible quantity. The chief obstacle to a- greater use of the gramophone as a source of broadcast entertainment at the present time seems to he the prejudice of listeners, carried over from the days when the shortcomings of the gramoplone were manifold, and broadcasting emphasised tather than minimised them. A COMBINED LOUDSPEAKER. N American has patented a combination of horn and cone _loudspeaker for ceiling fixing, two lampholders also being incorporated. Seund radiates equally in all directions. A "ELIMINATOR EFFICIENCY. "THE high efficiency of a new A eliminator fiiter that has appeared on the American market is due mainly to the tremendous capacity of the electrolytic condensers employed. ‘These have a capacity of several hundred thousand microfarads, obtained by virtue of thie usual arrangement of nickel and steel plates immersed in a non-acid caustic solution which constitutes the condenser. ‘he plates form one side of the condenser, and the solution the other. When an electric current is passed through the unit, infinitesimally thin films of hydrogen and oxygen form over the entire surface of the plates, and it is the thinness of this film dielectric that accounts. for the tremendous capacity obtained.. (End of Constructional Section.),