Radio Broadcast (May 1928-Apr 1929)

A RECEIVER OF STRIKING APPEARANCE The Sargent-Rayment receiver, with its aluminum cabinet and panel mounted upon a walnut base moulding, and blac\ control \nobs, presents an unusual and rather modern appearance which is perhaps more in \eeping with the electrical age which it typifies than the more conventional wooden cabinets. The gang condenser control is in the center, and the volume control at the right; the other five }{nobs control the individual trimming condensers for balancing exactly the r. f. stages The Sargent-Rayment Seven Receiver THE receiver described in this article is striking in that it departs successfully from many of the generally accepted tenets of home-built receiver design, and approaches the standards set by the higher priced factory-built sets costing up into the hundreds of dollars. It was developed by Messrs. Sargent and Rayment, the inventors of the Infradyne circuit which created considerable interest several years ago, and it embodies four individually shielded stages of t.r.f. amplification, a detector, and two audio stages of the Clough design. As it has several unusual features it is felt that a description of the salient engineering points of the design will be of interest to readers. From the photographs and diagram it is seen that the receiver consists of an aluminum shielding! assembly which serves the dual purpose of a cabinet for the entire receiver, and individual stage shielding for the different circuits of the set. This cabinet is made up of a pierced aluminum chassis, with the edges turned down, to which are fastened a number of smaller formed pans which serve as partitions, thus dividing the inside of the cabinet off into seven separate and distinct compartments. The assembly is completed by the front and back panels, which are bolted to the chassis and to all eight partitions, and finally by an aluminum cover, the edges of which are turned over to provide tight lap joints when the cover is placed on the receiver assembly. All of the metal work is of 7/64" aluminum, which provides most satisfactory electrical shielding. The complete shielding assembly alone uses nearly fourteen pounds of aluminum; the size is 27!" long. 125" wide, and 8i" high. In the picture on this page the receiver assembly is shown mounted upon a walnut base moulding which trims up the ap pearance so that the set would not look out of place in the average living room. The aluminum assembly is finished in attractive satin silver. Examination of the different illustrations and the circuit diagram in Fig. 1 shows that the amplification progresses from the antenna tuning circuit in the extreme left compartment of the aluminum shielding cabinet, through the four stages of tuned r.f. amplification to the detector in the sixth compartment. Four screen CT'HE names Sargent and Rayment are ■* probably familiar to many of our readers as the designers of the Infradyne, a receiver which has been described by our contemporary, Radio, on the Pacific Coast. The receiver described in this article is of the tuned radio-frequency type, employing four stages of r.f. amplification with type 222 tubes. The audio amplifier contains two transformer coupled stages. Although all the tuning condensers are controlled from a single dial, the set cannot truly be considered a single control receiver, for to obtain the maximum possible results the designers have placed small midget condensers across each tuned circuit. This, we feel, is a good idea, for it means that each circuit can be definitely adjusted to exact resonance. To put together a receiver containing this number of r.f. stages and have each stage in exact resonance with all the others throughout the entire broadcast band would necessitate exceedingly accurate coil and condenser matching. — The Editor. grid tubes are used in the r.f. stages, and a 201A, or preferably a 112A, for detector. In the extreme right compartment is housed the 2-stage audio amplifier and output transformer with the volume control. The center compartment of the receiver is left vacant except for the drum control dial which turns all five of the tuning condensers. All stage compartments are 12" deep, 6f " high, and 4J" wide. PERFORMANCE IN TESTS conducted upon different models of the Sargent-Rayment receiver during the period of its development, rather surprising results were obtained. On the West Coast, where the average receiver capable of giving adequate selectivity for other locations generally falls down quite badly, due to a number of peculiar local conditions, the Sargent-Rayment Seven has given positive 10-kc. selectivity — that is, it will separate distant stations ten kilocycles away from local broadcasters. As a specific instance, 10kc. separation was obtained on either side of kgo in Oakland, Cal., and in the same location krld of Dallas was brought in between kfi and kfrc. This is very exceptional operation in this locality. Such selectivity seems to leave little to be desired, for the receiver will go down to the noise level and bring in on the loud speaker any station sufficiently louder than atmospheric noises to be distinguished from it. To many radio fans this statement does not mean very much because upon the less sensitive receiver it is seldom indeed that the noise level observed is ever so loud as to drown out signals. This is not true of the Sargent-Rayment, for a simple turn of the volume control knob will increase its sensitivity to a point where weak atmospheric noises come in with a roar under conditions which would * 354