Radio broadcast .. (1922-30)

Record Details:

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In the R. B. Lab. 911 motion of the flux will induce an appreciable e.m.f. in the secondary coil if the coupling is sufficiently close. If regeneration is desired, this e.m.f. must be such as to place an -d.-A\tional positive charge on the grid which ass'scs the original charge. However, we know that an induced current is always in a direction opposite to that of the original or inducing current at moment of induction. This brings us to the very simply rule which may be relied upon to guide tickler connections rightly. Take any regenerative circuit, and consider two distinct currents as flowing from the tube, one from the grid, through the grid coil or secondary to the filament, and the other from the plate, through the plate coil and battery to the filament. (These conditions, in an electronic analysis, often exist during reception). The drawings in Fig. 6 illustrate this conception of the two individual currents flowing from the grid and plate of the tube, the arrows indicating the direction of flow as we have suggested. The rule is (bringing the coils close together) that these two currents must flow in opposing directions — i.e., one set of arrows must point up and the other set point down. The rule is further qualified as follows: When the coils are wound in the sane direction (A) either clockwise or counter clockwise, the grid must connect to the beginning of the grid coil and the plate to the end of the tickler or, of course, vice versa. When the coils are wound in opposite directions, the grid and plate should connect both to either the beginnings or ends of their respective coils. B, in Fig. 6, shows two coils wound in the same direction in which the requirement for regeneration has not been filled. The effect of this coupling, as explained, will be the opposite of regeneration. LABORATORY HINTS THE capacities of condensers used in radio circuits are generally given in microfarads, which means one millionth of the unit of capacity, the farad. The abbreviation for microfarad is "mfd." Thus, we often run across condenser specifications such as .001 or .0005 mfd. There has been a recent tendency to eliminate the decimal, and to consider these small capacities in micro-microfarads, or millionths of a microfarad. The abbreviation for this term is mmfd. Condensers having capacities of .00025 mfd., .00035 mfd. .0005 mfd. and .001 mfd. can be respectively described as 250 micro-microfarads, 350 micromicrofarads, 500 micro-microfarads, and 1000 micro-microfarads condensers. AN EXCELLENT reamer for working panel material is a round file, f inch in diameter at the large end. Enough of the tang is broken off so that the file can be grasped in a brace. Any hole in which the point of the file can be inserted can be reamed up to f inch by turning the brace FIG. 5 Rear view of the low-loss Roberts, using adapted Lopez Tuners. This set is particularly easy to neutralize