The 7B7 is a high impedance variable μ amplifier pentode. It was designed for RF & IF amplifier use, with a tuned anode circuit.
There are few places on the circular screen where a glimpse of the grids is possible.
The anode connection is a thick rod passing straight down to base pin 2 and is shielded by an extension of the main screen. This can be seen on the right.
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 58 mm tall.
References: Data-sheet & 1040. Type 7B7 was first introduced in 1940. See also1940 adverts.