The CV4009 is a special quality version of the CV454 and is also known as the 5749 and the 6BA6W. It is a variable μ pentode for use at HF. Most probably as RF amplifiers in radio receivers.
The anode hides the internal structure, however the tops of the grid supports are visible as is the anode screen below the lower mica.
The notches allow a view of the three wire grids.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins, is 52 mm long.
Reference: Data-sheet. Type CV4009 was first introduced in 1956. See also1956 adverts.
