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Show ( Edited by cl. Uougias Wardrop. Editor of Radio Merchandising-.) 2 TUBE CIRCUIT FOR DRY BATTERIES 2S0.M EKIOSTAT v t Aa- A-ct c- ,w. cwx . - Circuit Which Is Simple to Build and Simple to Operate. Incorporates Unique Features Seldom Found In Two-Control Outfit. 004 fUiO COWtliyt jl ! 5 Wtt, -y wm (On ) ' (UfiiV i sL ",t UN - ) ) J ' caiiij I 3 . p ) 1 45Tl;C 1 o 6 ir?n"''a Jr 906 455 AB- A-O C . 1 : Ratio of Transformer Should Be From Three to Six to One. Variable I Condenser Also Must Be of the Proper Capacity. By F. M. RUSSELL When a radio receiver is to be used in the home where it is operated by all members of the family, both young and old, it should possess certain features fea-tures such as simplicity in operation, perfectly clear and howlless reception, good receiving range, loud-speaking output, and a logged dial that eliminates elimi-nates the guess-work of tuning and makes it possible for one who never saw or heard the set before to get any station desired with It, by referring to the dial reading. The little two-tube set illustrated will do all the above things in an efficient manner. This Is due to the circuit used which is simple to build and simple to operate, but incorporates incorpor-ates several unique features that give it qualities seldom found in even a two-control outfit. It has automatic or spontaneous regeneration and an aperiodic primary. The regeneration increases volume and receiving range and the aperiodic primary" makes the set selective and allows lodging of the single tuning control. Never under any circumstances will the set howl if the parts are arranged correctly and the values are as specified. speci-fied. The secret of this is in the method of obtaining regeneration and the fixed condenser across the audiofrequency audio-frequency transformer. The readings of the variable condenser conden-ser dial, which is the only control, are permanent. If a station Is once received re-ceived at say 20 degrees it will always al-ways be received again at that point. This applies to distant as well' as local '. stations. Parts Used. The above re.su! ts are obtained by virtue of a special tuning unit in the form of a coupler. It consists of two splderweb coils, one of five turns and one of 45 turns. The five-turn coil Is the aperiodic primary and the other Is the combined plate and secondary coil. It Is not difficult to build the unit. Splderweb coils of the proper size can be purchased at a radio store or they can be home wound on a card-hoard card-hoard or wood frame. This should have 11, 13 or 15 spokes. The winding wind-ing method is two over anil two under. un-der. In other words, the wire Is first wound under two spokes and then over two spokes, etc. About one-half one-half pound of No. 11 double silk or cotton-covered wire Is necessary for this. Do not use enamel. To Construct. Mount the coils when finished as shown In the Illustration. The coupling cou-pling between them may vary anywhere any-where from one-quarter to one-half inch according to the selectivity desired. de-sired. I.ry out the sockets, transformer trans-former and the rest of the apparatus ns shown and wire with the direct connection method, that Is, make all connections direct from terminal to terminal in the shortest possible manner. man-ner. This may not look "pretty" but it will reduce the resistance and Inti-r-clrcult interference, and make the set more efficient. After all It's results we v. ant, not beauty. The parts necessary to construct the -it aside from the special coupler are as follous: ne .0;xi. variable condenser. one geared vend' r dial for condenser. con-denser. One low ratit audio frequency transformer. trans-former. fine .fidl fixed mien condenser. Two llrii type sockets. One 2."i-ohni rheosl at. One 2 to r-uiK'h in grid leak and .fiOO'J.I f'ix-d condenser. One 7 by 14 panel. One single-circuit Jack. I'.asehoard, binding posts, screws, wire, etc. 'Hie ratio of the transformer should he anywhere from three to six to one. but not higher. The set will distort If this Is violated. The variable con-dener con-dener ubio mint he of the proper rapacity. Any mnaller or larger will ajlther not allow the reception of cer tain wave lengths or bunch the st.v a turns up on half the capacity vana tion. Only one rheostat is used on both tubes. The adjustment on either is critical and a 25-ohm resistance will take care of them. The connections for I the .Oul fixed condenser are across the primary and secondary of the transformer to the I' and F posts. This must be placed in this position, not across the primary as is customary. custom-ary. To Tune Set. Tuning the set merely requires ad-Justing ad-Justing the rheostat and turning the dial. The stations will come in sometimes some-times without a carrier wave whistle, so It Is advisable to turn the dial very slowly and listen intently to be sure a station is not missed. On long distance dis-tance the adjustment Is apt to be critical. A geared vernier is essential because of jhis. Wfth the ordinary dial many stations would be passed up without the operator's knowledge. Boston Traveler. |