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A MIDGET ONE-TUBE REFLEX
A THIS issue of RADIO BROADCAST reaches the hands of the reader, it is just one year ago that we published the original article on the building of the single-tube reflex receiver — the "KnockOut." The passing year has seen the interest in this phenomenal receiver increase rather than wane, and while it is now essentially what it has always been — the finest one-tube set possible — suggestions from our readers and research in this laboratory have greatly increased the possibilities of the set. Almost every issue of IN THE R. B. LAB, since the article last November, has contained additional data on the construction and improved design of this receiver. The latest possibilities of the one-tube "Knock-Out" to be brought to our attention are embodied in the midget edition built by E. L. Faler, of Phoenix, Arizona, and are illustrated in the accompanying photographs.
The tuner unit is pictured in Figs, i and 2. This is primarily a vacation set. Compactness with the accompany ing ease of transportation was the first consideration of Mr. Faler. With the not incorrect idea that portability of this receiver varies indirectly with the size, he has greatly compressed.
What the Lab Offers You This Month
— How to build a midget one-tube reflex receiver according to the famous Knock-Out design.
— How to wind tiny inductances for a cigar box receiver.
—How to install pilot lamps to record the filament lighting of tubes in de luxe equipment.
— Facts about resistance-coupled amplification with dry cell tubes.
— How to choose the right rheostat for your tube.
— How to build an ultra efficient inductance: a combination honeycomb and spider web coil.
— Suggestions for the amateur laboratory.
— Hints on radio construction and operating.
The over-all dimensions of the set are approximately those of the average cigar-box. In fact, the designer started out with the definite idea of confining the set to this size, and the cabinet might well be one of these boxes improved with a little sandpapering and stain. A second cabinet, of the same size, was provided to hold the batteries — flashlight A cells for the uv-igg tube, and four small block B batteries.
Fig. 2 shows the back-of-panel construction and gives a general idea of how compactness is achieved. The radio transformers, Ti and T2, are the Midget Harkness coils manufactured by the Phoenix Radio Laboratories. A Hedgehog audio frequency amplifying transformer takes the place of the usually rather bulky T3, and the flat Variodon condensers are substituted for the conventional interleaving plate variables. This last, however, is a rather doubtful innovation, as the air condensers are necessarily more efficient and desirable. The interested constructor is advised^ to employ the usual 1 5-plate variable condenser, which, with the judicious placing of the remaining parts, should not increase the over-all dimensions of the receiver. An Erla fixed crystal is used in the detecting circuit.