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I have been promising a current test of some of the current production 12AX7 / ECC83 offerings and have just completed my testing.
Gain and Transconductance. Some folks confuse these two things. Maybe this will help explain:
Gain is the factor by which an amplifier multiplies a signal. It is the product of the output voltage at the plate divided by the input voltage at the control grid. Gain is a unit-less factor since both measured signals are voltages. (voltage)
Transconductance is a measurement of the ability of a tube to transmit current. It is the product of the output current in amps divided by the input voltage at the control grid. Transconductance is significant in that it shows us the difference in current capability that is generated by variations in plate impedance between tubes. (Current)
When I test tubes I also measure standing plate emissions current for preamp tubes that will be used in the phase inverter position. Plate current is one factor that many tube testers do not measure.
150 tubes were tested. 15 of each type. The above lines on each tube are the average of that particular tube.
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