Okay,
I've finally just a received a pair of Sylvania 6F6G tubes for the regulator and have had the system with the Sauvignon (Cortese Line Stage) running for around 2 hours now.
The Verdict: The system has not yet blown up, which is a good sign. The sound is little beefier, with certain instruments being brought out a little more. The extra deep bass maybe just a little too deep with the Ken Rads also plugged into the pre-amp. I suppose a more comprehensive listening test, with adaquate break-in time may make a difference.
Rectifier: Mullard GZ34
Regulator: Sylvania 6F6G with green letters
6SN7 : Ken Rad VT-231 Black Glass
Any thoughts as to this combination ? The Tung Sol Round Plates might make a better combination with the 6F6G. Although having said that, the Tung Sols are almost impossible to acquire here in Australia.