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Interesting. I think that with testing just for:

- gain
 - bias
 - distortion
 - power output
 - hum level balance

It is not necessary give an objective picture about resources of a tube. We can monitor the change rate in the tube bias as some of them change it as the tube get older, we can monitor distortion pattern change but we can do it only for a given tube to recognize how it ages. I was under impression, perhaps mistaken, that transconductance is the most objective evaluations criteria as it has voltages, current, gain and impedance melted together, I think it called transfer conductance sometimes…   I have two good testers but I do not measure transconductance for output tubes. My 6C33C out has different criteria that allows me to be more accurate then transconductance. But with the DHT tube I am confused how to measure then objectively. I think that the gain and bias, particularly with my cathode bias do not say anything about the state of tube. IT would show what brand and vintage have comparatively more current or gain but it would not indicate how much cathode emission was used for a given tube, not much cathode is poisoned and how much the tube is gassed.

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