The DL1 from Mullard is a dry cell audio output valve. It features a very low filament current and consequently a low audio output of 170 mW into a 22,000 Ω load. The envelope carries the printed Pentone trade mark as well as the BVA logo and manufacturing code 999 BF. The original box it was contained in gave the price of 9/- (nine Shillings).
The DL2 released the same year and both looking identical and sharing the same pin connections consumes twice the filament current. It also has a lower AC anode resistance and generates more power, in fact it can produce 240 mW. Still small but adequate from a wireless operating from dry cells.
Thanks to Stef Niewiadomski for sending the image.
The wide glass tube envelope is 30 mm in diameter, and excluding the Ct8 base pins is 82 mm tall.
Reference: 1043. Type DL1 was first introduced in 1939.
Absolute Maximum Operating Conditions¶
Updated December04, 2013.