• 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.

EML 20A capacitances

You can measure it. Build a simple stage and measure the high freq cut off frequency.
Then do the same with a 100k or 1M series R to the grid. The response will drop at a much lower freq and that will let you calculate the Miller cap.
Divide by the gain and you have the interelectrode cap.

Jan