The 6BA6 (also EF93) is a variable μ pentode for use at HF. Most probably as RF amplifiers in radio receivers.
The outer cylinder is the screen connected to the suppressor grid and the cathode. Through the notch can be seen the anode within as well as the three wire grids.
The base showing the screened anode connection, the copper supports for the control grid, the coiled heater wires and round cathode tube.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins, is 47 mm long.
References: Data-sheet & 1040. Type 6BA6 was first introduced in 1950. See also1950 adverts.
