This triode pentode was designed as a frequency changer for superhet receivers. The pentode has a high anode resistance and low mutual conductance, whilst the triode was designed for use as local oscillator.
This valve is essentially identical to the type AC/TP except for heater rating. A very robust Medium and Long Wave workhorse intended for simpler AC/DC superhets. Not intended for SW use.
The reverse is plain zinc paint.
The metallising seems to have detached around the top leaving the adhesive residue. Inside the wide cathode and wire grids can be seen. the triode would be mounted below the pentode section.
The classic envelope is 45 mm in diameter and, excluding the B9 base pins, is 102 mm tall.
References: Data-sheet & 1043. Type TP2620 was first introduced in 1934. See also1934 adverts.