The CV5172 is the UK service code for the DK92 miniature heptode frequency changer. These were used in dry battery powered receivers.
Domestic long and medium wave receivers would have this as the mixer to produce a 455 kHz IF from the incoming signal. It can be used with a separate oscillator, but was probably designed as a self oscillating mixer, in the manner of other pentagrid converters.
In this implementation the anode is cut-away at the sides.
The outer grids are helical but the inner grids pass flat across the filament.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 47 mm tall.
