The "Record" Short-Wave Receiver-Threevalve Set Fully Shielded

Radio Record, Volume I, Issue 21, 9 December 1927, Unnumbered Page

The "Record" Short-Wave Receiver-Three-valve Set Fully Shielded

May also be Constructed as a One-valve Converter

By

Megohm

With the increasing interest in short-wave reception from overseas, and the enlarging service available to listeners, readers will be interested in the following article on the construction of a fully-shielded three-valve Short-Wave Receiver, by "Megohm." The article describes a set which has actually been made and which is on exhibition in the Willis Street wi.dow of F. J. W. Fear & Co., Ltd., for a few days this week. A further section of the article will annear next week.

sam, HIS short-wave set has BEAL) been evolved by ‘Meg. i} ohm’? to provide construc- #| tors with a thoroughly reliable and sensitive complete short-wave set. The whole receiver is completely shielded in a copper case, easy of construction, which is recommended for use in towns and cities, or where there is any electrical interference. The shielding ensures a perfectly silent background, and cuts out quite an amount of noise that would otherwise detract from reception. The set gives good loudspeaker reception under favourable conditions of REFN, Chelmsford, PCJJ, KDKA, 2XAD, 2XAfP, etc., but of course not boisterous volume equal to that of tocal broadcast reception. ~° Results in Wellington have proved so good that constructors in laces more favourable to reception of ong-distance stations may look forward to recording some very fine achievements. There is no novelty in the actual circuit, which is a standard one that has given good, resuits over a long period in a set of a more experimental nature. GOOD COMPONENTS THROUGH: ouUT. The use of good components throughout ensures reliability of reception and quality amplification, particulurly having in view the fact that at no very distant date a short-wave set will probably be called upon to provide regular entertainment in the same way as does a broadcast receiver at the , -_

present time. The making of the coils is well within the scope of most amateurs, and with reasonable care in construction they will function absolutely as well as factory-made ones, But some may prefer to purchase readymade coils, and they will find several good makes on the market, COST OF MATERIALS, The following is a Jist of practically all materials required for the construc. tion of the set, not including valves :-

ALSO AS A CONVERTER.’ Although the provision of a complete set allows of short-wave reception under conditions too difiicnit for an unshielded set, some constructors may not care to go to the expense of a compiete receiver, and for that reason, after the description of the fall set has been riven, the making of the detector portion alone as an adaptor to plug in to a broadcast set detector valve holder, will be dealt with. By dispensing with the audio portion and the shielding, which is not mecessary on a converter, the saving in cost will be £2 19s., representing two transformers, two Klosner sockets, and copper sheet. Prices given are city prices, and purchasers will nat: urally expect to pay a little more for sonie lines in the country towns. The Diagrams. This week a plan of baseboard, view of tuning coils, and theoretical diagram are included. Next week a photographic reproduction of the rear view will be given, together with wiring under baseboard and other work. ing details. The main description will be concluded in the next issue. Looking at the front panel, which is copper sheet finished with black (Continued on Page 12.)

"Record" Short-Wave Set (Continued from Cover.)

cygle enamel, and backed with threeply, the secondary condenser dial is at the left, and lower down is the aerial coil control to alter the coupling. Near the centre is the reaction condenser dial, then the rtector rheostat, and at the extreme right two switches, one above the other, for A and B current. ‘The switches are handy, especially the B, as it allows of high-tension being quickly cut off before raising the shield to change coils. ‘The shield is designed to lift up quite easily, hinging on the back lower edge. Ll'our sets of coils, each set plugging in at one operation, cover must also be shielded, but this is done in a simple way that wili be described. For this reason connections to the set are made without the ortkodox array of terminals lined up on a shield, and form one cable to the box containing all batteries, A, B, and C. It is important that all components be spaced ont on the base in exactly the position shown, exact «neasurements being worked off with the accompanying scale. No earth connection is made to the set, but A positive must be connected to the front panel and bottom shield. The Tuning Coils. The aerial coil of three turns is permanent, and is three incues in diameter, wound with its own space of 18’s between each turn. Celluloid strips are put on inside and outside in three places, and fixed with cement made by dissolving chips of celluloid in liquid acetone. The coil ts bolted by its ends to two bolts in a piece of ebonite 2 by 1 5-8 inches, and the lower edge of this is screwed to a flat on a 8-S8ths dowel stick, that acts as a spindle to move the coil backwards and forwards. A light piece of flex is attached to each end of the coil; one of these goes to the aerial terminal, the other to moving plates of secondary condenser. There are four secondary coils, 8 inches in diameter, each a separate slip of ehonite, and each having attached am appropriate tickler of slightly smaller diameter, and 22’s enamelled wire. The aerial and secondary coils are made from 18’s bare tinned wire, specially suitable, as the tinning prevents corrosion of the surface. The ebonite mounting strips are 4} by 1 inch, and the piece supporting the aerial coi] is 1} wide by 1 5-8 high. (To be continued.) strip at the rear. The battery leadsall leave the set through the bottom) the short-wave band at present ir use. To give the shielding full effect, all leads between batteries and the set.

s. d. 6 6 & Hammarlund variable condensCL scceeecescececese were teesaeens 0 5 Accuratune vernier dial eesessacs 13

Other make of variahle condenser, with vernier , ..... Ferranti Al‘'3 audio transformer Igranic or other do. ...... Benjamin socket for 2 Klosner do. for audio ........ 2 SWitChHES .........cccccecseeeeeeesesees 30 ohms (Tgranic)... 1b. tinned 18’s coppér wire ... Ebonite for coils ceeeeeees @ vesceceece 4 sockets, 12 pins .......ccecceeeee Sheet 4ft. by 2ft. 28’s Wire for connections, celluloid, woodwork, screws, etc. ... Grid leak, Lynch, 7 megs Qs. 6d., Clips 6d... ceeeeeeeeeee Sangamo .0001 grid condenser S20 SF CROC OOAAaCEOOD

Connectors for condenser spinGleS ne eecccacececeesececereeeeees 04 0 2 fixed condensers, 1 mfd., each 4s. Yd. eee acess te-essnasoseneve » 09 G6 £718 6