The 2A3C is an audio power triode designed for high-end amplifier designs. The 2A3C like the original 2A3 is a directly heated valve. Unlike the original there is a single triode section in the envelope rather than two sections run in parallel.
The exhibit looks new and unused but there is no filament continuity.
This modern implementation has a ceramic base cap and gold plated pins. The maximum anode dissipation is 25 Watts and side flanges from the centre of the working face add extra radiating area.
There are four filament loops each with a coil spring to tension the wire.
The top mica with the coil tensioning springs. The hook holding the filament loop is within the anode cavity. The control grid is also kept within the long dimension of the anode.
The getter holder is down by the pinch stem leaving the main envelope crystal clear.
The rounded end of the anode.
The classic envelope is 58 mm in diameter, and excluding the UX4 base pins is 137 mm tall.
References: data-sheet. Type 2A3 was first introduced in 1935. See also1935 adverts.
