The UL44 is described by Mullard as a line timebase output pentode, what the Americans call a sweep tube. The 100 mA heater is for heater chain use, that is putting valves in series across the mains supply. A television is a complex device and normally required many valves and this is why the 300 mA chain became the standard. This valve was probably used for small black and white sets only.
The thin glass tube envelope is 20 mm in diameter, and excluding the B8A base pins, is 71 mm tall.
References: Datasheet & 1040. Type UL44 was first introduced in 1948.
Absolute Maximum Operating Conditions¶
Updated February 22, 2013.