The A410 from Philips is a dull emitter triode from the 1920s. The construction pattern follows that of the first European hard vacuum tubes with a single strand filament, helical grid and cylindrical anode mounted horizontally and all support fitted directly into the glass pinch.
The general construction and the silver gettering inside the top of the glass.
The relative diameters of the electrodes. The filament is held in place by a fold in the support wire.
The grid helix is welded to the support rod.
The grid looks to be fixed at every turn to the support. The simple anode is formed into a cylinder and then spot welded to the two supports.
The simple split pins set.
The method of anode construction leaves a small gap along the seam.
The balloon envelope is 42 mm in diameter and, excluding the B4 base pins, is 71 mm tall.
Reference: 3002. Type A410 was first introduced in 1924.