The Type 43, is an audio output pentode that is designed for use in receivers with a series heater chain. It is electrically identical to the IO based 25A6. The valve is rated for use in low power single ended output stages.
The electrodes. The black anode and three wire grids within. The control grid is wound on copper supports.
The copper g1 supports connect to a heat radiating fin above the top mica.
A side view of the anode cylinder. The support flanges are in the plane facing the camera. At the bottom of the image one can see the open helix of the suppressor grid with the closer wound screen grid within.
The classic envelope is 45 mm in diameter and, excluding the UX6 base pins, is 103 mm tall.
References: Data-sheet, 1040 & 1043. Type 43 was first introduced in 1932.