• 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.

CED/UNSET/CORONA-like ECC88 hybrid cascoded driver

Yes, I'm also sure that different tubes of the same kind will give different results too in reality. I need to define a BOM of other possible variations as well, then order all the needed from mouser.

The layout will be important too, because input and output are in phase.