Dating Sixtyfive reverb head

Hi, yesterday I bought my first MM amp and it's great. I think this sixtyfive reverb head is a late model with solid state preamp BUT the illustration sheet on the left side inside the amp says that my model "2275-65 ex" should have the 12AX7 preamp tube...any help on how identify this and dating the amp? Thank you!
Francesco

Transitional production. My 210-65 with the ss driver came from the factory with the schematic
for the 12AX7 version. They used what they had.
Think of it as a postage stamp made collectable
because of a small flaw. Or not.