The 6BY7 is a VHF varible μ pentode and is the counterpart to the EF80 straight RF pentode. Clearly this places the valve in a superhet context with AGC applied to the RF and IF sections in VHF/AM radio receivers and VHF television IFs.
The pentode section is considerably smaller than the envelope. The top half being given over to the getter.
The visible mesh is the screen. Other parts of the screening can be seen above and below the mica supports. Also there is a metal plate that drops to the base and covers the centre of the glass.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 58 mm tall.
References: Data-sheet & 1040. Type 6BY7 was first introduced in 1952.