The RC2 from Ediswan marks a point in valve development where the gain available allowed the use of Resistance - Capacitance coupling between stages. Prior to this intervalve transformers were required to make full use of the meagre gain available.
The electrodes are obscured by the silver gettering. The faint etched lettering can just be seen in daylight.
Dark-field lighting dramatically increases the legibility. The shadow effect is caused by the reflection of of the inner mirrored surface of the envelope.
I viewed looking up under the gettering the vertical cylindrical anode can be seen. The filament is a single strand and glows bright orange when lit, indicating a thoriated tungsten wire.
The balloon envelope is 37 mm in diameter, and excluding the B4 base pins is 97 mm tall.
References: Data-sheet & 1043. Type RC2 was first introduced in 1926. See also1926 adverts.