The R2018 is a general purpose triode with an unusual heater rating. 180 mA is not a common value for series heater chains.
We have a metalaised R2018 as well, plus the audio output triode P2018.
The anode side view. The anode is blackened - unusual for a low power valve. But the power valve P2018 looks identical, so a probable economy of scale.
The identification is etched into the dome of the envelope. The anode rating is given as 20 - 200 Volts. The words Barium tube remain but this valve is of modern construction and not a product of the older Azide process. Within the metal cathode tube is a small diameter ceramic tube and within that a slip coated heater.
The heater top connection connects to the side strut seen in the foreground here. Above the lower mica the grid can be seen.
A μ-Tracer plot of the characteristic curves for this exhibit.
The classic envelope is 37 mm in diameter, and excluding the B5 base pins is 96 mm tall.
Reference: 1043. Type R2018 was first introduced in 1932.