The SX-226 is a directly heated triode, also called the Type 26. The filament runs at 1.5 Volts and 1.05 Amps suggesting a bright emitter. The anode voltage is 180 Volts. These details were gleaned from an internet advert.
The face of the bright anode.
The triangular top mica. The filament is seen as an oxide coated ribbon. The tension spring runs top to bottom in the centre of the picture.
Tilted the grid becomes clearer.
The balloon envelope is 45 mm in diameter, and excluding the UX4 base pins is 99 mm tall.