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.
It is possible, but screen drive is not very linear and high driving level is required.
With 100 Vpp the output power is some 3,3 W (2k5 OPT), THD = 6 %
With 240 Vpp, 13 W, THD = 14 %. Distortion is mainly 2nd harmonic.
All the above values are from LT Spice simulation.
By connecting the cathode-resistor of the second triode to the first triode's cathode you get a positive feedback.The portion of feedback has to be less then the amplification of the first triode or else the circuit will oscillate.