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.
I have tried the usual IRF 140 kind, they work ok.
I am using STQ3N45 , small TO92, they sound 'finer'.
I will try also STU 3N45, the same as above but stouter. I think the TO92 is at its max possibilities in terms of Watts.