GE 12AX7A labeled "Fender Special Design" in red paint.
Round halo getter support.
Each plate is constructed of one piece of metal, folded and crimped together.  Note semicicular notch cut into open (unfolded) edge of plate. 
Plate is vented by rectangular cutouts at the top and bottom of the outside plate segments only. 

Etching is in "stencil" font:
12
AX7
A
U.S.A.
(pattern of dots)