The HP2018 is an RF pentode designed for use in universal or AC/DC mains broadcast receivers. The absence of the mains transformer limits the HT and this is why the low anode voltage.
This B5 base version was introduced in 1933, later the same year a B7 based version was issued. The screw top cap connection is typical of early 1930s practice.
The metal paint obscures the inner structure and the back of the envelope just states the country of origin.
To allow for all pentode electrodes to be connected. However, the reference does not give details of this valve with a side connection. In the B7 based version the suppressor grid does have a separate connection.
The classic envelope is 45 mm in diameter, and excluding the B5 base pins is 132 mm tall.
Reference: 1043. Type HP2018 was first introduced in 1932.