Voltage drop of various regulators in dc regulated power supply for preamp

[duderduderini]

hi guys.
Ok down to business.
I want to build the regulated supply psu shown.
It specifies 6z4 as a rectifier but i want to use either a gz34 or 5u4gb cause they are easier to get essentially.
The design specifies not to go too far over 300-0-300v for the transformer BUT this is with the 6z4..
I have found that the GZ34 drops voltage by 25V and the 5u4gb 50V and by my research the 6z4 doesnt drop voltage much.
If you note Kevin Braun(the author of that design) specifies about 367 V coming off the rectifier before a cap input filter.
I wont be using that high an input cap .. either 60uF for the GZ34 or 100uF for the 5u4 GB.
And yes i have used Duncans PSU designer but quite honestly I dont get accurate results cause I dont know how to measure some of the parameters that must be inputed.
So essentially I need some help to determine the Output of the Tranny prior to filtering with either the GZ34 or 5U4GB
I will be running two of these boards for L and R channels but will use the one transformer(these cost a bunch in Australia)
Thankyou for your help.
I tried to include the schematic but of course its too big...
http://eshop.diyclub.biz/article_info.php?articles_id=3
Regards
Nick