The ATP7 is the UK Army pre-CV designation for the HF Pentode that was based on the V226. After 1941 it was renamed the CV1368 when all UK Government valve procurement was harmonised.
The ATP7 is a selected Mazda V226 where the selection is that the mutual conductance is a minimum of 3.0.
Internally the three wire grids can be seen within the oval sheet metal anode. The valve is directly heated with an oxide coated filament, the filament passes through the electrodes four times.
A closer look at the top of the anode and the oxide coated filament. The helical top tensioning springs are obscured and are under the screen.
The classic envelope is 45 mm in diameter and, excluding the B7 base pins, is 124 mm tall.