Looking at a basic design for the amp, I started with the F2a operating points. See the curves below. The loadline is at 7k5, operating point at 375V on the plate, 70mA bias current and grid bias at -16V. The approximate power is around 3W. This requires a driver stage that can swing 32 V peak to peak. Not a bad set of parameters.
Now, I wouldn't read too much into this, as the formulas are only approximations and the curves are only approximations and the determination of the various points are only approximations. But, it does give some confirmation that this is a good starting point.
One might be thinking that it is a pretty expensive way to get 3Wrms of power with the plate disspation at 26W. Perhaps a different load line is required, this might warrant a 5k or 3.5k loadline to get more juice out of this tube. More to follow.