The VT75A is a war time development of the television line output valve type KT44. It is fitted with a B7 base as was the KT44. The 'T' variant was designed for a slightly higher maximum anode voltage. It is not clear if the use was as part of the RF chain or the modulation side of a transmitter. The VT designation clearly marks this as a transmitting valve for the RAF.
The fact that this is marked VT75A indicates that it was made for the RAF and as such the specification would have been available to several makers, the UK government would not be restricted to a single source of supply. Our other VT75A is marked as an M-OV valve and so this is probably not.
The anode assembly: The control grid is wound on copper supports and has large heat radiating fins on the top (left side of image). On the right can just be seen the bright right-angled beam forming plate.
Looking up into the lower mica support it can be seen that the screen grid support is quite close to the beam-forming plate.
The classic envelope is 57 mm in diameter and, excluding the B7 base pins, is 137 mm tall.
References: 1043. Type VT75A was first introduced in 1939. See also1939 adverts.