Radio age (Jan 1927-Jan 1928)

RADIO AGE for October, 1927 Back panel and baseboard view of the Thompson Super Seven, showing the compact and neat arrangements of parts The Thompson Super Seven Incorporating the Latest Ideas in Tone Quality and Selectivity By SIDNEY J. THOMPSON IN DESIGNING the seven-tube super described in this article the two main objectives were to devise a superheterodyne receiver which would possess the excellent qualities expected of this most interesting of radio receiving instruments but which would combine this satisfactory result with a low cost. Considerable experimental work was done and many intermediate transformers were tried. Some of these were low-priced transformers which were immediately discarded because of their lack of ability to reach the standard demanded by the designer for this receiver. It finally appeared that the only alternative was to produce a super that could deliver the goods but to proceed blindfolded, List of Parts for the Thompson Super Seven 1 Silver Marshall No. 340 Midget Condenser $ 1.50 6 Silver Marshall Tube Sockets, 50c ea 3.00 2 Silver Marshall Drum Type Dials No. 805, $3.00 ea 6.00 1 Pair Silver Marshall Brackets 70 1 Yaxley Filament Switch 50 2 Yaxley Imp. Jacks, 25c pr 25 1 Yaxley 2 L Resistance 15 1 Yaxley 3 L Resistance 15 1 Yaxley 30 Ohm Rheostat 1.35 1 Tobe .006 Condenser 45 1 Tobe 1 mfd. Condenser 90 1 Tobe .002 Condenser 40 1 Tobe .00025 Condenser 35 1 Tobe .001 Condenser 40 2 Halldorson Precision Iron Core No. 540 Transformers, $6.00 ea 12.00 1 Halldorson Precision No. 541 Filter Transformer 6.00 2 Halldorson Overtone Audio Transformers, $6.00 ea 12.00 1 Halldorson Overtone Output Transformers 6.00 1 7x21 Panel drilled and engraved 3.40 1 9x20 sub panel drilled and engraved 4.95 1 3 meg. gridleak 50 1 Resistor Mounting 35 2 Camfield .0005 mfd. Condensers, $6.00 ea 12.00 10 X. L. Spring Binding Posts 15c ea _ 1.50 1 Ellis Oscillator Coupler 3.00 1 Spring Socket 75 Total $78.55 When aerial and ground operation is desired in preference to a loop. Use — 1 No. 2 Ellis Antenna Coupler $ 3.00 so far as cost was concerned. This would have defeated us in trying to reach one of our chief objectives. As a last resort, several manufacturers of high grade products were called upon and the cooperation of their engineering staffs requested. Then there began an elimination contest which was to result finally in the selection of a combination of quality parts to produce the two desired results. No attention whatsoever was paid to the products used, for the engineers were instructed to produce the finest reasonably priced superheterodyne that could be built with quality products. Tonal Quality and Overtones Let us consider what is required to produce true rendition of the original broadcast. It is not a difficult matter to obtain excellent high note reproduction, likewise it is not difficult to obtain excellent low note reproduction. Audio amplifying systems can be developed to accentuate either high or low notes. In a great many cases it is more pleasing to accentuate, for instance, the low base notes. To some this accentuation gives a soft deep tone that is rather pleasing. Other tastes for music frequently vary the other way, preference being given to accentuation of the higher notes. Obviously, neither one of these systems can produce perfect reproduction of the original broadcast and neither one would satisfy a trained musician. The perfect audio system then would be one wherein the loud speaker and the Audio Transformers were so balanced that a flat amplification curve is obtained not for the Audio system alone nor for the loud speaker, but for the entire combination of receiving set and speaker. The output from the loud speaker should represent, in other words, a perfectly flat