The 6SN7GT double triode valve is electrically equal to a pair of the 6J5 triodes in a single envelope.
The envelope also has an etched identification. This form of octogon is typical of RCA and can be seen on 6SN7GT. Could it be that this is not quite the Cossor valve it says it is?
The twin triodes - end elevation.
The anode in close-up revealing the fine pitch grid wire and multiple heater strands.
The wide glass tube envelope is 29 mm in diameter and excluding the IO base pin length, stands 63 mm high.
References: Data-sheet, 1040 & 1043. Type 6SN7GT was first introduced in 1941. See also1941 adverts.