The 41MTA is a purpose designed high μ triode for use in television timebase circuits. The 41MTB was a triode for push-pull timebase circuits.
The identification on the dome gives the Cossor name, the BVA logo, Made in England and the code V7.
This image reveals a pair of grid windings. The inner grid is shaped to be close to the cathode. The outer grid passes flat in front of the anode. Close inspection shows that within an outer metal frame the working faces of the anode are made of mesh. It is not clear how the inner grid is connected.
The classic envelope is 50 mm in diameter, and excluding the B5 base pins is 113 mm tall.
Reference: 1043. Type 41MTA was first introduced in 1937.