With a winding of 400V and a rectified voltage of 565V max, we will have a dissipation of about 100W in the power tubes at 0V 200mA.
If we have a winding 230V, or 325V rectified, we can do 2 ranges: one from 0 to 320V and one from 280 to 450V.
The anodic dissipation at 200mA will then be: range 1, 60W max, range 2, 40W max, which is quite reasonable and even allows to envisage a current greater than 200 mA.
I reject the custom transformer solution because it is not applicable for many.
The other transformers:
For 6.3V heating of the power tubes, a 6V transformer can be used.
For the supply of G2 of power tubes (I will explain later why it MUST be pentode, and not triode) , it is possible to use a 6V / 110V + 110V transformer powered by the 6V winding of the power tubes heating transformer.
One of the 110V secondary will be used for the G2 supply, the other to generate the negative bias voltage if the isolation level between the 110V windings is sufficient.
For the heating of the other tubes, another small 6V transformer
All these transformers are easily found.
To be continued....