The 63SPT was A C Cossor's type designation number for the EF50s that it made and this example is a UK product and features the Cossor green paint on the aluminium can.
We also have a 63SPT made in the US for Cossor.
The valve was so important during WWII that several manufacturers were involved although the design was a breakthrough for Philips in The Netherlands.
The code reads, MB1BE6.
The rest of the can is plain aluminium protecting the glass valve within.
The wide metal tube envelope is 33 mm in diameter and, excluding the B9A base pins, is 60 mm tall.
References: Data-sheet & 1043. Type 63SPT was first introduced in 1938.