The Osram HL210 was first introduced in 1928 and is a general purpose triode.
The etching on the face of the envelope is difficult to read and very hard to photograph. The Type designation is on the dome and is almost invisible.
The designation is in two lines. The 2 is legible but the rest of the 210 is very hard to read. On the first line only the second vertical of the H can be found. By comparing with other HL210's it was possible to see the first line vertical was in the same place as more legible HL210's.
Even with enhancement the type is almost invisible.
The horizontal anode. The grid wires can just be seen on the full size image.
The balloon envelope is 41 mm in diameter and, excluding the B4 base pins, is 75 mm tall.
References: Data-sheet & 1043. Type HL210 was first introduced in 1929. See also1929 adverts.
