I have been using a 250VA Hammond Industrial Control Transformer running on a variac at 80VAC to achieve the needed 400VDC of B+ for a SE DC 6AQ5 project amplifier I have been developing over recent months. While this method of using the variac works well , it is only a temporary solution.
On the AES website, I found a Hammond PT that might work with a tube rectifier and the flywheel filter while providing the correct B+ voltage.
I ran a PSUD2 simulation with the flywheel filter as seen in the above posted screen capture.
The Hammond part # is P-T273BX : 700VCT 182VA 5V 3A 6.3VCT 5A
The part can be sourced at Antique Electronics Supply for $95.99 with free shipping.