The DRD as Jack Elliano shows it calls for 700V B+. It can be as low as about 550V and still have room to direct couple, so that is something to keep in mind.

To get 700V With a standard full wave rectfier will require about 1100VAC ! 550-0-550. This is doable especially if we use damper diodes but it means haveing a custom transformer made.

On the other hand, If we use a full wave bridge, solid state or hybred. We can get the necessary voltage with a standard 750V (375-0-375), 800V (400-0-400) and a choke input filter. I am kind of likeing this idea as these transformers are pretty thick on the ground, from the likes of Hammond, One Electron, Angela and just about everyone else. You might have a pair in stock, or can be recycled from an old project. (I know I do)

The next consideration is what we need for filaments. First off for this amp I am going to uas DC, or some sort of current reg for the 300b. The best I have been able to get with AC is about 5-6mv of noise. not too bad but I want better. This means at least one secondary at ~1.5A,6.3VAC , maybe more.