The W3 from Cossor is a dull emitter audio output valve from 1925 and features an oxide-coated filament. The base is 32 mm in diameter.
The envelope has the Cossor name etched at an angle and the Type designation and operating details etched horizontally. The paper label is a transcription of the envelope lettering.
The top of the envelope allows a view of the anode and also shows that this valve never had any green paint on it. Our other W3 has the paint and the box it came in shows clearly the paint was a feature of the branding. One can only speculate as to why this valve was never painted.
The wide glass tube envelope is 28 mm in diameter, and excluding the B4 base pins is 82 mm tall.
References: 1003 & 1004. Type W3 was first introduced in 1925.