The MSG/LA is a tetrode from the early mains valve era with its 4 Volt heater and it offered a higher mutual conductance than the MSG/HA. It would be used for RF amplification in broadcast radio receivers.
The plain zinc paint on the reverse.
The screw top cap that was used until the top-hat style took over in the mid 1930s.
The balloon envelope is 44 mm in diameter and, excluding the B5 base pins, is 125 mm tall.
References: Datasheet & 1040. Type MSG/LA was first introduced in 1931.