The 6BN11 Compactron houses a pair of straight or sharp cut-off pentodes. These are designed for IF amplification in American television receivers.
The anodes have a maximum dissipation of 3.1 Watts. In normal service each pentode would run with 125 Volts on the anode and draw 11 mA with a grid bias of -3 Volts. In this configuration the gm is 13 mA/V and the anode AC resistance ra is 0.2 MΩ.
The dome carries the Type identification.
Here the name Admiral can just be made out. Within the anode the suppressor grid support can be seen.
The 12 pin B12C Duodecar base.
The wide glass tube envelope is 28 mm in diameter, and excluding the base pins is 50 mm tall.
Reference: Datasheet. Type 6BN11 was first introduced in 1965.