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Some old testers (1930s) tested tubes that way. A small battery was used to apply a steady voltage to the grid, then you would compare plate current on the meter as the battery was switched on and off. It was called the 'grid shift' method. Basically it gave you two points on The operating curve. A tube with a worn out cathode would produce less shift in current, and ones with grid issues such as shorts would also not show a normal grid shift.
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