The DAF91 is a diode pentode valve was designed for battery portable radio receivers. This short grid base pentode was designed with particular reference to AF voltage amplification. The 1.4 Volt filament is to be run from a dry cell and the 90 Volt anode rating matches standard HT batteries.
The device was specified by Mullard for use as a detector and first audio amplifier.
The bright anode of the pentode with the single diode above.
The thick support on the left connects to the getter holder and the filament tension spring.
The single strand oxide coated filament passes through the diode and then the pentode.
The thin glass tube envelope measures 18 mm in diameter and the excluding the B7G base pins, is 46 mm tall.
References: Data-sheet & 1040. Type DAF91 was first introduced in 1946.