The 6BE6 is a heptode or pentagrid valve. The heptode is classically used as a frequency changer in a superhet receiver.
Radio and Television both use the superhet principle. To change frequency the incoming signal is mixed with a local oscillator. The electron stream is effectively switched on and off by the oscillator. In practice the process is one of producing sum and difference frequencies via a non linear response rather than just mixing of two signals linearly.
To prevent the oscillator and the signal interfering in unplanned ways a screening grid keeps the circuits apart.
The RCA name and the end of the suppressor grid seen through the gaps in the anode.
The suppressor grid is easy to see but with care the mass of wire grids can be seen.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
References: Data-sheet & 1040. Type 6BE6 was first introduced in 1950.