The N17 is an audio output pentode designed for battery portable radio receivers in the late 1940s. The output power is very small at just over a quarter of a Watt so a high efficiency loud speaker would be required, probably of limited fidelity.
The Osram branding label on this M-OV valve.
The plain anode cylinder encloses all of the electrodes.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins it is 45 mm in length.
References: Data-sheet & 1040. Type N17 was first introduced in 1949.