Basic Radio is a free introductory textbook on electronics based on tubes. See the editorial for more information.... |
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Scaling CircuitsAuthor: J.B. Hoag It is sometimes desired to count a succession of impulses occurring more rapidly than can be followed by even the most delicately constructed mechanical counter. Then one may use a modification of the inverter circuit so that the mechanical counter is operated by every other input impulse. Such circuits are consequently called scale-of-two circuits. Furthermore, by cascading a number of scale-of-two circuits, scale-of-four, -eight, -sixteen, and -thirty-two counters have been built. In the last case the mechanical counter's reading is to be multiplied by thirty-two to give the actual input number of impulses.
A second impulse, positive on A, starts tube 1 and, in so doing, shuts off tube 2, resetting meter M. Thus the meter counts every other impulse. When several scale-of-two circuits are connected in cascade and the counting rate becomes very high, the necessary de-ionization time of the first stage gas-filled tubes limits the frequency response of the unit. In addition, gas-filled tubes are notably subject to temperature variations. Hence it has been considered desirable to devise a scale-of-two circuit, using vacuum rather than gas-filled tubes. A circuit of this type1 is described in the next section.
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