The 33 is a battery audio output pentode. Under normal conditions, operating as a single ended class A amplifier the output is 700 mW.
The Tung-Sol name and on the right can be seen the letters VT as this is also marked VT-33 for the USA Government procurement code.
The low power valve does not need the anode to be blackened for superior heat radiating properties. The three wire grids can be seen and the vertical rod connects to the filament tension spring.
The view into the top shows the single inverted V oxide coated filament.
The filament tension spring at the top and the suppressor grid has a more open pitch than the other grids - as expected. The suppressor grid can be seen to have copper supports.
The classic envelope is 45 mm in diameter and, excluding the UX5 base pins, is 100 mm tall.
References: Data-sheet, 1040 & 1043. Type 33 was first introduced in 1936. See also1936 adverts.
