In the case of series-current feedback, it is convenient to describe the gain of the open-loop amplifier in terms of mutual conductance.

This is often exploited in R.F. amplifiers where an alteration of the grid bias changes the mutual conductance and hence the gain of the device.

All of our tubes are all tested for hot & cold shorts, leakage, emmision, plate current, & mutual conductance (& matched where applicable).

Transconductance (for transfer conductance), also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device per the voltage across the input of a device.

Sharp-cutoff ("high slope" or ordinary) pentodes have the more ordinary uniform spacing of grid wires, and so mutual conductance decreases in an essentially uniform manner with increasing negative bias, and has a more abrupt cutoff.

The mutual conductance tester tests the tube dynamically by applying bias and an AC voltage to the control grid, and measuring the current obtained on the plate, while maintaining the correct DC voltages on the plate and screen grid.