"1.5," "1.6," "1.7," and "1.9" do not appear to me to be representative of filament draw. The 5751 is listed in my older GE tube manual as drawing 0.175 amps at 12.6 volts. If the 1.5 were amps, it would mean nearly 19 watts filament dissipation, which is obviously wrong for a low power dual triode. I don't know what those numbers would represent.
That tube manual lists gm (transconductance, also referred to as mutual conductance) for the 5751 as 1200, without specifying whether that is average, minimum, etc. My Hickok 800A tube tester lists 1250, specifying that as being for an "average tube," NOT an "average new tube," which it indicates will "be higher." So 1300/1350 would seem to be reasonably good numbers, while 1640/1740 sounds excellent, although the difference between the two sets of numbers leads me to question how well matched they are. The numbers before and after the slash, btw, I would assume are for each of the two triode sections within the tube.
HTH,
-- Al
That tube manual lists gm (transconductance, also referred to as mutual conductance) for the 5751 as 1200, without specifying whether that is average, minimum, etc. My Hickok 800A tube tester lists 1250, specifying that as being for an "average tube," NOT an "average new tube," which it indicates will "be higher." So 1300/1350 would seem to be reasonably good numbers, while 1640/1740 sounds excellent, although the difference between the two sets of numbers leads me to question how well matched they are. The numbers before and after the slash, btw, I would assume are for each of the two triode sections within the tube.
HTH,
-- Al