. Electronic apparatus for biological research . HT=300 Figure B' along a path parallel to AB, as the voltage drop across the resistance increases. At the end of the sweep the total deflector coil voltage is Lt -\- imsixR = 200 V, leaving an anode voltage for the valve of 100 V. From the foregoing the points to watch in design emerge; they are: (1) B must not move outside the maximum power hyperbola; (2) B' must not move outside the working region at the knees of the anode characteristics; (3) neither B nor B' must go above the maximum anode current line. The parallelogram ABB'A' is a pr
. Electronic apparatus for biological research . HT=300 Figure B' along a path parallel to AB, as the voltage drop across the resistance increases. At the end of the sweep the total deflector coil voltage is Lt -\- imsixR = 200 V, leaving an anode voltage for the valve of 100 V. From the foregoing the points to watch in design emerge; they are: (1) B must not move outside the maximum power hyperbola; (2) B' must not move outside the working region at the knees of the anode characteristics; (3) neither B nor B' must go above the maximum anode current line. The parallelogram ABB'A' is a property of the particular deflector coil used and the upper and lower sweep speeds. It may be drawn on tracing paper and juggled about on the anode characteristics for various valves until one is found which it will neatly fit. The quiescent bias and HT+ voltage required are then determined. If the parallelogram cannot be made to fit because Pmax or /a_niax for the valve is infringed, consider using two valves in parallel. This halves the current each has to supply and also, incidentally, since g„^ has been doubled, halves the amplitude of input wave required at the grid. If it cannot be made to fit because no valve will stand the amount of HT required, a new deflector coil having fewer turns is indicated. For example, if we halve the number of turns, the inductance L will be reduced to one quarter, /will have to be doubled, so the back , Li, will be halved. The input wave ampHtude will also in general require doubling. The extra current required by the new coil may require two valves in parallel in place of one, in which case the input required remains the same. Negative current feedback The linearity of the output current depends on the constant-current genera- tor living up to its name. The pentode is entitled to be regarded as a constant- current generator in virtue of its high internal resistance /-„, of the order of a 249
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