. Electronic apparatus for biological research . Figure tubes in order so that those with the greatest difference between their running and striking voltages are at the bottom and those with the least are at the top. Now take a set of high resistances, in number one less than the number of tubes, the lowest of the order of megohms and of values such that each is, say, 5 times the value of its predecessor. 2 megohms and 10 megohms would be suitable for a chain of 3 tubes. Connect them as in Figure Now consider what happens when K„ is connected. Let the running vohages of the tubes be F
. Electronic apparatus for biological research . Figure tubes in order so that those with the greatest difference between their running and striking voltages are at the bottom and those with the least are at the top. Now take a set of high resistances, in number one less than the number of tubes, the lowest of the order of megohms and of values such that each is, say, 5 times the value of its predecessor. 2 megohms and 10 megohms would be suitable for a chain of 3 tubes. Connect them as in Figure Now consider what happens when K„ is connected. Let the running vohages of the tubes be Fj, Kg and V^. At first the whole of F„ is applied to the bottom, most refractory tube by way of the high resistances, ensuring that it strikes. Then we have K„ — Fg applied to the upper two tubes, but because of the potential divider now made by the resistances, I of it is applied to V^, ensuring that it strikes. Finally we have K„ — (Kg + V<^ applied to the upper, least refractory tube, and this will strike if F„ — (Kg + Kg) is greater than its striking voltage, or if F„ — (Kj + Kg + Kg) exceeds the voltage differential of this tube. The rule is that the tubes will strike if the difference between the unstabilized input and the stabilized output voltages exceeds the difference between the running and striking voltages of the least refractory tube, provided the tubes are arranged to strike in the right order. Having found K,,min, we can look about for some point in the power pack from which to tap off F„. Stabilizers are not perfect and in fact there is some change of voltage across them when the glow current changes, so that as far as increments of voltage and current are concerned they may be allotted an equivalent resistance. Thus if a reference tube voltage changes from 69-9 to 70-1 volts for a glow current change from i to 1| miUiamps, its incremental resistance is 0-2/10"^ = 200 ohms. Note that this is a non- linear device and the incremental
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