Dear Robert Lyness,
Sorry for the delay in my response. It seems that I can not reach you by
normal e-mail and therefore I use the server. (hope it is allowed) Thank
you for your reaction to my questions about soldering Au/Sn. My
experience closely matches yours in that I find 330 degrees C  works
well as a soldering temperature. Do you mean that 15%  H2 works
better than 10%? The hotplate I am using is an OFHC Cu plate heated by
W wires.  It works well. What I still have not found out is what the
required dew point of the gas should be.
Thank you again for your response.
Frik Koch