RADIO DESIGN IMPROVES

Radio Record, 20 May 1938, Page 70

RADIO DESIGN IMPROVES

Iron-Cored Cores Win Their Spurs. Smaller Sets — Prove Most Popular During 1937-36

-URING the past year ironcored coils have definitely proved their worth, so much so that they have practically displaced the air-core types-especially in the I.F. amplifier stages. These iron-cores have been developed to give better selectivity and gain in otherwisé standard circuits, and in I.F. amplifier transformers, where the frequency of operation is fixed, their properties can be used to best advantage. Of the home-constructed sets, or kit-sets, four and five-valve receivers have taken the lead and this has been responsible for the fact that the majority of sets described in the "N.Z. Radio Times" during the past year have not been above six valves. Expense and the desire tu get the best possible results froni the smallest possible number of valves seem to have been mainly responsible for this. Both the above factors played a big part in compiling this yeat's "Radio Constructors’ Guide." but though most of the receivers described in it are not of more than five valves, they cover all types, portables, super portables, super regenerative, reflexed, broadcast. dualwave, allwave and pretuned-hoth A.C. and battery operated. However, all ‘the sets desctibed in the 1938 "Radio Guide" are not small ones. T'wenty-one actual receivers are included in this i issue, as against thirteen described last year. They range’ from | one to eight valves and cover. all ty pes: . For the first time, a pretuned receiver is described as a kit-set.. On test, this receiver gave excellent reaults and, although only a four-

valve set, when: pretuned to Australian stations it brought them in with a remarkable degree of accuracy in tuning. Instructions are-also given for converting this receiver into. a dualwave set. The usual selection of instru-. ments is in evidence. foremost among them being a cathode ray oscillograph and a wide-range multimeter. An enlarged section ot charts, tables and valve data is included, the valve data portion list-. ing American and European type valves (both metal -and glass), as well as selected equipment types. The "Royal" Cathode Ray Oscillograph, .which proved so popular when described in .the "‘N.Z. Radio Times" last year, has been included in the "Guide" and should prove 4 great help to experimenters and servicemen in tracking faults and interference. This oscillograph uses a 913 cathode ray tube, with a diameter of one inch and, although the screen is small, the tracings are particularly clear. (See above.) This vear the book has not been split up into sections as formerly, but has been divided into two por-tions-one containing receivers, instruments, and general technical articles, and the other containing the charts, tables and valve data. This method has been adopted because, nowadays, the demarcation between different types of sets or between, receivers aud instruments is not as :pronounced as was formerly the case.. The charts, etc., however, have been separated from the main body of the hook to ‘forin’a reference section on all phases of radio, calculation. The grouping ‘of the advertise-

ments into a "Buyer’s Guide," in the 1937 issue, proved so popular that this practice has been: adopted in _this year’s issue-also. For ‘quick reference to any particular type of radio component.or receiver, the indexing of the components, etc., by types, has proved invaluable. The "Buyer’s Guide" is printed on coloured paper and stapled in the centre of the book-and order forms are included in it! | po Some subjects which have heen included each year have been ‘excluded from this issue to avoid overduplicating and to make room for new material: Nevertheless, readers can rest assured that the -best possible use has been made of the space available. The 1938 "Radio Constructors’ Guide". is well. up to the standard of previous issues, and from the point of view of the receivers described, it is the best effort yet!