. QST . A front view of the S-FS Indicator. The zero-adjustcontrol is to the right of the toggle switch. Si. Themeter registers either signal or field strength, dependingupon the setting of the toggle switch. nected in parallel and then, through a singlelead, to J2. Fig. 1 shows heater wiring for both6- and 12-volt operation. Pin 9 of the tube is notused in the 12-volt circuit. For S-meter operation, the meter and R2 areswitched across the cathode terminals of thetube by Si. The 500-ohm potentiometer, R2,becomes a zero-adjust control. Zero reading isobtained -nath R2 adjusted for equal voltage
. QST . A front view of the S-FS Indicator. The zero-adjustcontrol is to the right of the toggle switch. Si. Themeter registers either signal or field strength, dependingupon the setting of the toggle switch. nected in parallel and then, through a singlelead, to J2. Fig. 1 shows heater wiring for both6- and 12-volt operation. Pin 9 of the tube is notused in the 12-volt circuit. For S-meter operation, the meter and R2 areswitched across the cathode terminals of thetube by Si. The 500-ohm potentiometer, R2,becomes a zero-adjust control. Zero reading isobtained -nath R2 adjusted for equal voltageat Pms 3 and 8 of the 12AX7. After an initialzero adjustment, the application of voltagethrough Ri will drive the cathode of Fia nega-tive with respect to the cathode of F2B, thusupsetting the meter balance and causing anupward deflection. For a given voltage. September 1955 19. the amplitude of the deflection will l)e controlledby Ri. The S-FS Indicator uses a Type 12AX7 inpreference to the 6SN7 employed by W0WLRbecause it draws considerably less plate saving is important if power for the S-meter,as well as the converter, is taken from the The 6SN7 and its prototype (12BH7)will work well in the circuit, but only at theexpense of increased current drain. The circuit of the field-strength section iselectrically equivalent to the one describedpreviously.^ It is made active by switching themeter and R2 into the circuit and by through Ji. The amount of fed to the cir-cuit may be controlled bj^ adjusting the lengthof the pick-up antenna attached to Ji. R2 is ashunt to prevent off-scale readings when measur-ing strong fields. Con struc Hon As shown in the top view, the Triplett model227-T meter is mounted on the front panel ofthe utility box. If the meter is centered with itstop edge 1^ inches down from the top of t
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectradio, bookyear1915
