The 6AU6 is a sharp cut-off RF pentode for use up to 50 MHz. Also this valve can be used at audio or as a limiter or sync. separator.
This valve was made by Mullard for the American distributor IEC and carries both company names.
The Mullard name and the fact that it was made in the UK.
The wire grids seen through the end wall of the anode. The control grid is wound on copper supports for better heat conduction away from the working area.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins the valve is 46 mm tall.
References: Data-sheet & 4054. Type 6AU6 was first introduced in 1946. See also1946 adverts.