By FRANK L. BRITTIN
Selectivity, achieved with a minimum of controls, has been the aim of circuit designers for some time, in a set of the tuned r.f. type. In the six-tube set described in this article, selectivity and sensitivity have been attained by the use of specially designed coils and a well-balanced circuit without adding any more controls than absolutely necessary. These coils are similar in construction to the low-loss coils employed in the 15 to 550-meter set. described in the November, 1926, issue, but are of the stationary instead of the plug-in type.
{{c|Rear View of Completed Set, Showing Simple Arrangement of Parts and Method of Wiring above Subpanel
The set employs three stages of r.f. amplification, and has two controls of the modern drum type, facilitating easy operation of the set. A separate tuning condenser is used for the first r.f. stage, permitting perfect tuning, regardless of the length of aerial used. The detector and two stages of transformer-coupled a.f. amplification, with power-tube equipment in the last stage, complete the circuit. If all tuning controls were grouped for operation with one dial, an ideal condition would be realized, but, if this is done, it would be difficult to obtain perfect matching of the tuning units over the entire waveband. It would be possible to bring the receiver into perfect resonance at one wavelength on the dial, but on turning the dial to other wavelengths, this would not be true. Another point taken into consideration by the designer was the matching
