The DE25HF does not carry a makers name but was made by Quikko. The type two BBC stamp places the date of manufacture between September 1924 and 1927.
Initially the details we had about this exhibit come from the paper label on the ribbed base. The design purpose was as a detector or an R-C coupled (RCC) amplifier.
The BBC stamp is a paper circle stuck to the glass. The anode has flat sides and a rounded top. The filament is a single horizontal strand. The grid is formed from hoops fixed to two horizontal supports.
A closer look at the grid suggests a flat plate that has been punched to leave thin strips between the ends. The sheet has subsequently been folded to shape.
The balloon envelope is 42 mm in diameter, and excluding the B4 base pins is 104 mm tall.
References: 1043. Type DE25HF was first introduced in 1926.