Radio Broadcast (May-Oct 1926)

OCTOBER, 1926 WHAT'S NEW AT THE RADIO SHOWS 521 ceivers. Among others making two Control receivers are All-American, Argus, Bosch, Bosworth. Bremer-Tully, Case, Gilfillan, Stewart-Warner, Valley, Workside and the A-C Dayton, the latter employing two additional controls, used only when very precise tuning is attempted. All single-control receivers are not alike. Among them are represented several degrees of convenience and perfection in design. Some sets have a single master control, combined with extra compensating controls to take care of slight variations in the calibration of the circuits. Other receivers are made with such accuracy and so expertly calibrated under laboratory conditions that no compensating adjustments are needed. Still others are equipped with frictionally coupled or closely spaced controls so that they may be used singly or in unison at the will of the operator. Included in these two groups are models from Bosch, Bosworth, Dunn, Grebe, Radiola, and others. THE GRAND CALIBRATED DIAL ANOTHER feature which distinguishes these various single-control receivers is the method used in calibrating the indicator. Some are so accurately built that the tuning dial is marked, by the maker, in wavelengths or even by the call letters of the principal stations. Others have drums upon which the user himself indicates the stations, when the receiver is installed in its permanent location. Still others are marked in arbitrary units, such as 1 to 100. Obviously it is a great advantage to the novice to be able to set the receiver to a desired wavelength, according to dial markings. This feature has been incorporated in the products of the Apex, Bosch, Fada, Freed-Eisemann, Kolster, Magnavox, Pfanstiehl, Priess, Shamrock, Stewart Warner, and a number of others. The receiving set may be divided into THE PERLESZ SINGLE-CONTROL RECEIVER An unusual eight-tube new model presented for this season. The attractive cabinet contains a built-in speaker and space for current supply THE FRESHMAN MASTERPIECE CONSOLE MODEL Freshman continues his three-control receiver, thus helping to maintain the proportion of threecontrol to the other types. A built-in speaker is a feature of this moderately priced set three parts, (1) The radio-frequency amplifier, (2) the detector circuit and (3) the audio-frequency amplifier. The engineers designing 1927 products have given considerable attention to the importance of properly dividing the work among these three departments of the receiver. To accomplish this, many have completely shielded each tube circuit so that it would not affect its neighbor in doing its work. By using several stages of radio-frequency amplification, sufficient energy is delivered to the detector, even with loop pick-up, to operate the detector tube without introducing distortion. Overloading the detector, when listening to near-by, high power stations, or using a long antenna, is avoided by the use of a volume control, reducing the amplification of one radio-frequency tube. The functioning of the detector tube has been aided materially by such design because the tube no longer must deal altogether with signals of greatly varied strength. The audio-frequency channel also gains by the new balance of functioning introduced by these methods. An audiofrequency amplifier, regardless of type, works with minimum distortion if the tubes are passing normal plate current. If the filament emission is reduced by means of a rheostat, to avoid overloading, the tonal quality is seriously thinned. Likewise, too strong a signal produces the all-toofamiliar blasting. The use of a volume control in an early radio-frequency stage, used for several years in the Radiola superheterodyne, has been adopted by manv manufacturers this year. Another feature which makes for good tonal quality is the operation of vacuum tubes with the correct filament and plate potentials. No matter how skillfully a manufacturer makes his set, its tone output in the hands of the user is not good unless the proper A, B, and C voltages are applied to the vacuum tubes. This problem is aggravated by the fact that many socket power devices deliver different voltages under different load conditions, making it difficult to be certain of the voltage applied. B, and C batteries likewise suffer a gradual fall in voltage as they are used. Distortion sometimes creeps in so gradually that the regular user is not aware of change in quality. Many manufacturers have incorporated voltmeters in their sets or have provided pin jacks so that voltmeters can be installed easily at the option of the purchaser. These meters enable the set user to maintain his tube filaments at the proper voltage. An interesting feature of the FreedEisemann receiver is a switching mechanism by which the plate voltage applied to each tube on the set may be read instantly, as well as that of the A battery at its terminals (giving warning that the battery needs recharging), at the filament terminals (permitting the prolongation of tube life to the maximum by the use of correct voltage) and the various C battery voltages in the audio amplifier. The Radiola super-heterodyne loop receiver has been long established in the field, but with 1927 come several worthy competitors. By successfully coupling four THE CROSLEY 5-75 A new model in the Crosley line. Like many of this year's models, the set has a single station selector, with space for writing in stations heard. The set has a built-in reproducer and ample room for batteries. Price $75.