The Cossor Stentor Six, dating from 1927, was later issued as the Cossor 610P audio output valve. It has a μ of 8 and was designed for a load of 9,000 Ω.
The gettering hides the inner structure.
The main operating parameters are printed on the paper label.
The balloon envelope is 45 mm in diameter and, excluding the B4 base pins, is 96 mm tall.
References: Data, 1043 & 1040. Type Stentor Six was first introduced in 1927. See also1927 adverts.