The ECF82 is a high slope triode pentode designed for television use as a frequency changer or mixer. It was also found to be effective as an audio phase splitter.
The anode opposite the grid support rods is open allowing a limited view inside. The bright structure is the beam forming plate. The ECF82 is a beam tetrode.
The pentode on the left is much larger than the triode on the right. The lettering states British Made and also Made in Canada.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 47 mm tall.
References: Data-sheet & 1040 Type ECF82 was first introduced in 1953. See also1953 adverts.