The 2A3 is an audio power triode that is still used in amplifier designs. Modern manufacture reproduces this directly heated design.
The 2A3 is normally used in a push-pull arrangement and care needs to be taken in the bias settings for each valve as a small change in grid bias will greatly alter the standing anode current and any mismatch will impair the reproduction quality.
This example has two triode assemblies within a common anode. The sections are connected in parallel internally. This arrangement is believed to date to the 1940s.
The etched inscription is very faint but this enhanced image shows the ID lozenge and the fact that it was made by Westinghouse Canada.
The two filament assemblies can be seen. The anode has two oval bays but is formed as a single unit.
A clearer view of the two anode sections with a common central web.
The lower mica: in the foreground is one triode with the filament seen as four vertical strands. The background is an identical structure.
The classic envelope is 51 mm in diameter, and excluding the UX4 base pins is 121 mm tall.
References: data-sheet. Type 2A3 was first introduced in 1936.