GB620757A - Improvements in or relating to apparatus for measuring mutual conductance - Google Patents

Abstract

620,757. Measuring mutual conductance. SANGAMO WESTON, Ltd. March 19, 1946, No. 8555. Convention date, Oct. 31, 1945. [Class 37] For measuring the mutual conductance of a valve the anode and grid are supplied with A.C. of different frequencies. A transformer T has a primary winding 1 and secondary windings 2, 3, 4, 12 for supplying energizing potentials to the valve B to be tested and to a signal source A for generating a higher frequency signal voltage. A series inductor 5 is included in the anode circuit of the valve B and is shunted by a resistor 6 in series with a condenser 7 having a low impedance at the signal voltage frequency. The voltage drop across the inductor 5 develops a current in the resistor 6 that is measured by a rectifier meter 8 in series with a resistor 9. The grid signal generator A includes a triode 11 and grid and anode inductances 13, 14 coupled by a magnetic core 15. The anode voltage is supplied from the secondary winding 4 through a switch 17. A winding 23 on the core 15 is connected across a resistor 24, which is connected between the grid of the valve B and the grid-biasing secondary 3 of the transformer T. A tap switch 25 permits adjustment of the magnitude of the signal voltage applied to the grid of the valve B. The signal voltage generator A is operative only during those halfcycles during which the anodes of the valves 11, B are positive with respect to their cathodes, and generates pulses of comparatively high frequency (e.g. 5 kilocycles for a power line frequency of 50 to 60 cycles per second). The values of the inductor 5 and condenser 7 are so chosen that the low-frequency anode current is excluded from the meter 8, which measures the current of signal frequency and may be calibrated directly in values of mutual conductance if the voltage source is substantially constant. D.C. potentials may be applied to the grid, screen, and suppressor electrodes of the valve B, with A.C. applied to the anode through a frequency selective network. The same D.C. may be employed for energizing the signal voltage generator.