Tips and Jottings

Radio Record, Volume II, Issue 10, 21 September 1928, Page 29

Tips and Jottings

The Double-Roll Loud-Speaker. "V_EGOuM" Will be pleased to hear from constructors of this speaker as to its performance. It is undoubtedly capable of very fine reproduction, giving more even amplification through the scale than is the case with many speakers. A Coil-Driven Loud-Speaker. A VERY fine example of the dynamic or coil-driven loud-speaker is now being demonstrated. at. the "International Radio Company’s premises, Wellington. The Kolster Power Speaker is enclosed in a handsome console cabinet with grille and gauze front. In addition to:the speaker it-

self, there is included a B eliminator, which excites the field magnet and also supplies B.current for the receiver. A two-stage transformer-coupled amplifier is also included in the cabinet, a 7: watt tube being employed in the last stage. The eliminator must supply a comparatively heavy current, and is therefore equipped with two UX281] half-wave rectifying tubes, and in addition there is a ballast tube to compensate for variations in line voltage. The whole outfit operates by connection with the A.C. mains. Needless to say, reproduction is very ‘fine. Radio Parts Direct From Factory. (THE General Radio Company, Cambridge, Mass. U.S.A., recently instituted a system of dealing direct with the consumer, and as they manufacture many lines of interest exclusively to experimenters, an opportunity is presented to the latter of obtaining apparatus that would otherwise be very difficult to acquire. cptemicsient

Paint Earth Plate Contacts. THIN an earth wire is soldered to a metal plate to form a buried earth plate, the joint should be thickly painted or tarred in order to lengthen the life of the joint. This precaution is especially neessary when tins or thin iron plates are used. Holes in Sheet Metal. IFFICULTY igs sometimes experienced in drilling holes in sheet metal used for interstage screening, especially if the material is thin. As a rule it will be found easier to punch the hole; provided a soft metal such as copper or aluminium is used there is no need for any special tool, as a rod of steel or: even brass with one end filed square will serve quite well. It is essential, however, that the sheet in which the hole is to be made should be rested on the end grain of a piece of hard wood or similar material. . iniidnttanten