This directly triode has the electrodes mounted at an angle and the envelope lettering is in red paint. The lettering is damaged but a ZA.7.3 seems to be present. On the other side can be made out the letter R and in front of the R is just visible the left leg of a cap A. STC made only one triode in this period on a UY base with an AR suffix and this was the 4022AR. The data-sheet seems to confirm this identification.
The remaining lettering with the A and R. Within the anode is a W shaped filament. The STC 4101DS has the same style of lettering and STC were the UK arm of Western Electric and also concerned with telephone systems.
A closer view of the anode showing the grid winding and the filament tension springs.
The balloon envelope is 56 mm in diameter, and excluding the UV base pins is 102 mm tall.
References: Data-sheet & 1043. Type 4022AR was first introduced in 1925. See also1925 adverts.