Radio age (Jan 1927-Jan 1928)

RADIO AGE for October, 1927 mounting sockets, which directly become a part of the sub-base. These sockets and the Selectone units are so spaced as to make the plate and grid leads very short and convenient. Eight Selectone series B units comprise the essential of this receiver, and these units can be identified as the Selectone B-530 Antenna-Coupler (looking from left to right on the photograph Figure 2) directly followed by the two Selectone B-S20 RF Units, next a Selectone B-500 Intermediate Frequency Transformer, a Selectone B-510 Filter, another B-500 followed by a second B510, which feeds the second dectector with amplified signal. These new units are the heart of the World's Record Super 10, and are the result of more than five years of constant test and experiment in an effort to obtain optimum in efficiency, appearance and sensitivity. Housed in highly polished bakelite casings, all of the same appearance, they stand majestically like soldiers in a row, each of them designed to do their utmost in intercepting and amplifying faithfully weak and distant signals as well as those of local transmitters. The oscillator unit designated as Selectone B-540, sets between the two Remler drum controlled condensers. The selectivity enables the operator to tune in stations far away through heavy local interference, with ten kilocycle separation on all but the nearest ones, when a slightly greater margin must be allowed to avoid background noise. All these new units are laboratory matched products. While the World's Record Super 10 is a receiver made of laboratory equipment, it must not be considered as an experiment. Each unit is closely matched and peaked, and every Selectone unit is held to a rigid standard of performance, uniformity and efficiency. The assembly of such units into a working component is obviously rewarded with crowning and brilliant result. The New Selectone B-530 and B-520 RF Couplers are manufactured with as much precision and care as though each were going to be used in a highly important piece of test equipment. The winding of the coils is done in the most careful manner as to insure high efficiency and amplification. The assembly into cases is supervised closely by engineers to detect irregularities and defects, and when completed, the units are subjected to the gruelling test of a device that detects inequalities of more than one third of a turn of wire on the coil. In this test the coils are matched to a uniformity of less than one turn, and so that the secondary inductance is practically the same. The Lorenz type of winding, is used in the RF Couplers, and the cases are so placed that losses are at a minimum. Referring to the circuit diagram, in blueprint, it will be noted that the RF Couplers are stabilized by the voltage drop across the rheostat, limiting the electronic emission from filament to plate, that is, increasing or decreasing the working efficiency of the tubes. The coils themselves are proportioned and designed to adapt themselves to this method of control so that no difficulty is experienced in obtaining stability with good tone and maximum efficiency. The pickup coil of the oscillator is located in the grid lead of the first detector, where it has been found most efficient. A grid leak and detector is used in the frequency changer, and a proper adjustment of this detector tube avails great 15 sensitivity for the pickup stages. One of the departures from accepted procedure is evident in the grid return of the frequency changing tube (first detector). This has been made negative instead of positive as is customary, research disclosing that this is the best connection. A Remler RF Choke in the plate lead of the tube keeps RF strays from filtering into the Intermediate train where they might be troublesome.. This brings us to the Selectone B-500 Intermediate Frequency transformer, the first in the IF train, then to the Selectone B-510 and thus on to the second detector tube, which is activated by the secondary of the B-510 connected to its grid circuit. The intermediate stages themselves are not radical in their connections, the refinements having been restricted to the Intermediate Transformers themselves. The tubes are kept at the exact amplification point by the proper ratio of primary to secondary, and the relative spacing of the coils which governs stability, amplification and tone. The amplifier in entirety is stabilized by the 400 ohm Carter potentiometer which is connected in the usual fashion across the A negative and A positive filament potential. Many radio enthusiasts fail to fully appreciate the importance of good intermediate frequency transformers, which explains generally why the super-hetrodyne has been long considered as a complicated and difficult receiver to construct and operate satisfactorily. This erroneous conception is far from true. If the Intermediate Frequency transformers are really matched for peak frequency, regeneration and amplification, and if they are intelligently designed and wound to give Fig. 3. Bottom view of the superheterodyne showing simplicity and neatness of wiring