WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Most tubes will not show a correct bias when first turned on. A 45 minute run time seems to be a good average of warm up before measurements are valid. I have no idea if this is what you wanted, but there it is.