The ECL80 is a triode, output pentode for audio use. ECL80 is a low power device for building a compact single end low power audio stage. The ECL80 was much used in domestic television receivers in the 1950's and early 1960's.
The ECL80 was not without faults in use and the above article gives details.
Elpico was a UK distributor and the green ink looks to be the colour used by Cossor.
The stacked sections on the common cathode. The top triode is oriented at right angles to the pentode. There is a coating on the inside of the glass opposite the hole in the end wall of the anode. Like the EF91 coating this would reduce the chance of electron bombardment evolving gas from the glass.
The triode with extended anode plates for greater heat removal.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 57 mm tall.
References: Data-sheet & 1040. Type ECL80 was first introduced in 1950.