Thanks for the detailed reply. Mine is not a Signature model. By looking at the font on the top of the unit, it's probably more of a "first-generation' type. What KT88's did you eventually land on?
I'm searching for a good local technician so hopefully I can fine someone that's not only competent, but not backed up 6 months!
I emailed Cary this morning to see the costs and turn-around time for the F1 upgrade. We'll see what they have to say.