The UD2 is an audio output triode. Triotron describe it as a Super Power type at a time when a quarter of a Watt could seem loud.
The first set of operating conditions relate to its introduction in 1927 and the second set to the improved version from 1933.
Triotron made a series of output valves with various power output ratings. ZD2 had the lowest power rising to SP2 with the greatest. The series was: ZD2, UD2, YD2 & SP2. A similar series existed for four volt valves.
The paper label gives the dealer's name and the sale date of 31 March 1934.
The identification is feint and etched into the dome.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 87 mm tall.
References: 1043 & Advert Type UD2 was first introduced in 1927.