RADIO AND ITS RECEIVERS

Sun (Auckland), Volume II, Issue 546, 26 December 1928, Page 14

RADIO AND ITS RECEIVERS

Conducted for THE SUN by

R. F. HAYCOCK.

GLASS PANELS MAKING SETS ORNAMENTAL The use of glass as a panel is generally avoided by amateurs on account of the supposed difficulty in handling it. It must be admitted, in fact, that the amateur who likes to experiment with his set, and who contemplates adding to or altering any of the panel components, would be well advised to stick to ebonite. But the experimenter who intends his set to be both permanent and ornamental, and who is prepared to take a little more care than usual, will find that glass offers many advantages over the more orthodox panel. In the first place it ranks with the best ebonite as regards insulating properties, and it is far superior to the cheap and shoddy ebonite that is sometimes sold. In use it will not deteriorate like ebonite and will always present a neat appearance, in contrast to ebonite, which sometimes fades in a short time. LIKE FRAMING A PICTURE To obtain the best results, more than usual care must be taken in preparing the panel, and it may be necessary to modify to some degree the layout of your set. Suppose, for example, you have a cabinet, American style, with front inside measurements 16in by Bin (an ordinary size for two-valve cabinets). You will require about sft of picture beading. The dimensions of the glass will depend upon the width of this beading. The glass should be 14 Jin by 6sin. Briefly, in fact, we proceed merely! as in framing a picture, the outside frame measurements to be 16in by Sin. with the glass taking the place of the picture. The beading cut to length, the corners should be mitred with extreme care. Every care should be taken to ensure that the frame is a perfec-; fit into the cabinet. The frame made, we can turn our attention to drilling the glass. HOW TO DRILL In order to lighten this part of the task, it is best to bring all terminals to an ebonite strip at the rear, even at the cost of altering the layout. This done, the average owner will find that he has onlv three, or perhaps four, holes to drill, each perhaps 3-Bin in diameter. Place the glass on a perfectly flat surface, to obviate all risks of breaking or scratching it. A geared drill is preferable, as the drilling must be done slowly. The ouestion of drills is of paramount importance. Ordinary drills are useless. Specially prepared drills can sometimes be obtained, but personally I prefer three-cornered flies, ground smooth and pointed. Drill slowlv. bearing gently but firmly. For large hole it is best to drill an 1-Sin guide hole, as it proves quicker in the end. A comnound of camphor and turpentine applied to the point of the drill will help matters considerably. while ordinary oil is better than nothing. The drills should be sharpened frequently with a small file. When half-way through, turn the glass and recommence on the opposite side. The glass drilled, it can be placed in the frame and fastening strips screwed on. It is not essential to mitre these, but the top of the strip should not protrude above the level of the beading on the other side of the glass. Small brackets may be fixed on the corners, as shown. All fixing strips and brackets should, of course, be screwed from the inside. The panel should now be ready for fixing to the baseboard. The constructor can judge for himself the number and size of the screws, but it is generally wise to add angle brackets, whatever the size of the panel. To aid the neat appearance, beading of a similar nature should be fixed round the edges of the cabinet. Special care should be taken with the wiring; covered wire being advocated. Unless you are extremely hardy with the soldering iron, it is preferable to screw all joints, and the wiring, as far as possible, should be kept at the back of the set. When fixing your components to the panel it is advisable to place a thin leather washer between the glass and the fixing hut. In any case, do not screw up too tightly.

“N.Z. RADIO HANDBOOK” A GUIDE FOR LISTENERS No. 6 of the N.Z. Radio Handbook contains a host of articles which listeners will find invaluable. For those who have not yet taken up the fascinating hobby of radio, a very interesting article, “What Set Shall I Buy?” should prove of great assistance. There are several constructional plans of various apparatus. One In particular, “The Homebuilder’s Crystal Set,” is certain to attract the interest of those who desire to make a cheap and efficient crystal set. For those who want to learn Morse with a minimum of trouble, there is described a new method of committing the symbols to memory. Many other articles of interest not only to the radio new chums, but to the experienced radio fan, will be found in the handbook, which Is fully up to the standard of its predecessors. PORTMANTEAU VALVES How many readers, I wonder, have had any experience of multiple valves? At present these are made in two patterns. The triple valve Incorporates in one and the same bulb, a rectifier and two L.F. valves, the second of which is of the power type. The glass contains also all the necessary condensers, resistances and so on, to form the inter-valve couplings. Owing to the extremely short connections that can then be used, many advantages including increased stability-—are obtained. Set construction becomes a matter of the utmost simplicity. You yoke a coil and a condenser to one end of the valve and a loud-speaker to the other. Having connected up the batteries you find that you havts produced a three-valve receiver! The triple valve has, however, one drawback. Since there is no H.F. amplification before the rectifier and since reaction cannot be used, it is necessarily a short-range contrivance, suitable chiefly for receiving the broadcasts of the local station up to twenty miles or so. A dual H.F. valve is also made, which can be employed in conjunction with the triple. With the pair you obtain an ultra-simple five-valver of fair efficiency. Since both the multiple valves and receiving sets incorporating them are now to be made in this country, we shall, no doubt, see and hear a great deal more of them in the future.