Cossor describe the 210DET as a battery triode for use as a detector where a fairly large signal may be expected.
The envelope is screened with zinc loaded metallic paint.
The disc holds the wire to the glass so that the metal paint makes good contact.
The dome carries the Cossor name, BVA, Made in England and the code V9. The latter is often mistaken for a type designation in valves where the main identification was a paper label.
The Balloon envelope is 41 mm in diameter and, excluding the B$ base pins, is 83 mm tall.
References: Data-sheet & Data. Type 210DET was first introduced in 1930. See also1930 adverts.
