The 5725 is a special quality vibration resistant RF pentode. The overprint 5725W indicates the special quality version.
The box anode folded and stitched at the side flange.
The grids are not that clear in this image but looking at the valve, the control grid looks to be gold plated with the screen grid aligned to the same pitch. The suppressor grid has a close pitch and thus could be used as a secondary control element and the data-sheet gives a mutual conductance for g3.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 38 mm tall.
Reference: Data-sheet. Type 5725 was first introduced in 1950. See also1950 adverts.
