The 6159 is the 6146 with a 300 mA heater. It is a small transmitting beam tetrode valve normally used in pairs within HF transmitters of 100 W output.
The side view.
The anode is carbonised and has fins as extra radiators.
The base is standard International Octal but the valve skirt and envelope are wider than the standard base.
The wide glass tube envelope is 38 mm in diameter and excluding the IO base pins, the valve is 80 mm.
Reference: Data-sheet. Type 6159 was first introduced in 1952. See also1952 adverts.