The 3A/144A is a directly heated triode with a five Watt anode dissipation. The prototype was the 4104D. It is a replacement for use in older telephone repeaters. The old GPO code is POVT132. The UV base is of the bayonet type and so the pins are solid and a location pip is inserted into the side of the base cap.
KB/F would identify this valve as being made to specification K1001 or K1006, the B would denote qualification by a UK authority and the F identifies the maker as STC, Paignton. Here just the F is printed to give the factory as the STC logo appears on the valve.
The filament is oxide coated whereas the 4101D was a bright emitter. The serial number is 79. Three tension springs can be seen at the top.
The CV1694 designation appears on the other side of the envelope. The bright anode is a plain box.
Looking into the top of the valve shows the oxide coated filament and the control grid winding.
The classic envelope is 44 mm in diameter, and excluding the UV base pins is 101 mm tall.
Reference: Data-sheet. Type 3A/144A was first introduced in 1946. See also1946 adverts.
