The 6V7G is a double diode triode for use in superhet receivers. The diodes act as AGC and signal detectors and the amplifier triode would act as the first AF stage.
The 6V7G is on an IO base but electrically identical to the type 85 that is on a UX6 base. The type 55 is on a UX6 base and differs only to the extent that the heater is 2.5 Volts at 1 Amp.
Thanks to Marcus for sending in the picture.
The classic envelope is 38 mm in diameter, and excluding the IO base pins is 100 mm tall.
References: Datasheet, 1040 & 1043. Type 6V7G was first introduced in 1937.
Absolute Maximum Operating Conditions¶
Updated January 08, 2013.