• 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.

How does one determine saturation point of triode or pentode

I take it your mostly a solid state guy. Cutoff and saturation with tubes is more of a gradual thing than an absolute point. Except perhaps the saturation point in some Pentode applications. For most cases, the point on the load line where the grid to cathode voltage equals 0V is the pseudo "saturation". But in actuality most sources can drive the tubes grid slightly positive.

But generally when designing, draw the loadline and use the Vgc = 0V as the point of saturation.