The ZD17 is a diode pentode valve was designed for battery portable radio receivers where the diode acts as the signal detector and the amplifier pentode is the first audio stage. This short grid base pentode was designed with particular reference to audio amplification.
The 1.4 Volt filament is to be run from a dry cell and the 90 Volt anode rating matches standard HT batteries.
The Osram brand label on this M-OV valve.
The pentode three wire grids can be seen. The filament is a single oxide coated strand. The small box at the top is the single diode anode.
The thin glass tube envelope measures 18 mm in diameter and the excluding the B7G base pins, is 44 mm tall.
Reference: Data-sheet. Type ZD17 was first introduced in 1953.