I will convert my Fisher 400 to 6BL8 phase inverters. This is a time consuming job and will be a sinful departure from factory stock. I may use Mullard E80CF (6BL8 related). These Mullard E80CF tubes will be installed in the Scott 340B. You can try them in your TA-800 too.
Sounds interesting, I'm not changing a thing in the TA-800 though. Playing some Joe Satriani today with the 800 hooked to my Frazier MK IV's, just freaking crazy good!