Sensibly equivalent¶ to:
The 1AC6 is the Cossor designation for the Mullard DK92 and as can be seen from the envelope the two are identical.
The valve is a miniature heptode frequency changer for use in dry battery powered radio 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.
The reverse shows little detail.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 45 mm tall.
References: Datasheet & 1040
Absolute Maximum Operating Conditions¶
Updated January 18, 2013. shape:thin.glass.tube construction:all.glass type:heptode age:1940.1950 base:b7g heater:1.4v pins:7 pin:1.f+ pin:2.a pin:3.g2 pin:4.g1 pin:5.g4 pin:6.g3 pin:7.f-.g5