hey-Hey!!!, Here is the link to the schematic: http://www.audioroundtable.com/GroupBuild/Projects/Galahad_Bias_Doubler_Schematic.pdf
The unloaded AC voltage of the supply TX should be very close to 30. AC voltge * 2 * root2 needs to be always less than the PIV of the diodes used. There are Schottky of higher voltage, so uprating is fairly easy. cheers, Douglas