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Or you might try this: build the HV supply, make a voltage divider to create about +75V, then connect that to the center tap of the 6.3V winding. Run the heaters on AC with this elevated filament winding and I bet you'll get plenty quiet results. NY Dave did that on one of his mic preamp designs, and your signal voltages will be a lot higher.Peace,Paul
Unfortunately, those international power supplies only go up to 250V