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.
As the bias winding doesn't need to be tied to GND, you'd use a Delon doubler. It's output impedance will be sufficiently low for the purpose.
Best regards!