The 17DW4A is a half wave rectifier designed for use as an efficiency diode in monochrome television receivers. There are a family of these rectifiers with the 6BS3A as the 6.3 Volt base design. The 12BS3A/12DW4A has a 12.6 Volt heater and the 17BS3A/17DW4A version has a 16.8 Volt heater. The 17DW4A would be used within a 450 mA series heater chain.
The anode is made from two sheets stitched together and blackened on the outer surface.
The edge of the anode showing the inner surfaces.
The base end. The heater is the two thinner insulated wires and the thicker insulated wire is formed as a helical spacer between the heater and cathode wall to improve the heater/cathode breakdown voltage.
The top of the valve shows even more clearly the helical spacer between the heater and the cathode tube.
The wide glass tube envelope is 28 mm in diameter, and excluding the B9D base pins is 66 mm tall.