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Show Constants of Wave Meter Should Not Change in Use It is essential that the constants of a wave meter should not change in use. Some slight difficulty has been experienced with vacuum tube wave meters, owing to the necessity of substituting sub-stituting a new tube when the original origi-nal one, with which the instrument was calibrated, burns out. Varying inter-electrode capacities of the tubes, for example, would seriousiy alter the maximum wave length to which the wave meter will tune, thereby introducing intro-ducing inaccuracies over the whole of the range. Col. K. E. foigeworth describes de-scribes in his (British) patent a circuit cir-cuit which overcomes this difficulty. Here it will be seen that a tube V is ; israuimie l: 1 Wave Meter Circuit That Holds Its Calibration if Tube Is Changed. ! provided with a tickler coil LI and a "I!" battery. This is coupled in the normal manner to a grid circuit in- ductance L2. tuned by a variable con- j denser line end A of the indue- tance 1.2 is connected to the filament ! F of the tube; while instead of con- j necting the free end D directly to the ' grid of the Tube, the actual grid con- ; nootion is taken to a tapping point X j along the inductance 1.2. so that only a portion of the turns of the indue- j lance are actually in the grid circuit. ', Obviously, then, the tube capacity is . in shaut only with a few of the turns 1 instead of all the turns, as would bo the c:!se with rl.e normal iM-raogo-m.nt. This imnir - ': miy s:;.':t variation in ik'h' c;.; y wiil not : a-t-'viai'y aip'r ti-o wave hr.gih o' ' ' . oi:-'-a:r 1.2 " : :n'c the - a pa. '.' y va- ia-ti.ci ia-ti.ci is only in si-aim wirli a few of the turns. 1... tahni Virc!es YYo.M. |