The D-1 from Philips is a bright emitter triode from 1920 and was made in Holland. it is also known as the D1. The basic operating information is etched into the glass envelope. Radiomuseum states that it is a gas filled triode for use as a detector. The RAF Type D is of the same period and is also a gas filled or soft triode.
The lettering is 3.5 V, 20-25 V and Importe de Hollande.
The anode cylinder and the single strand filament running through the centre.
The control grid is helical and fixed loop by loop to the single support wire.
The electrodes. The filament is held in a fold of the support as tungsten has too high a melting point to weld.
A μ-Tracer plot of the valve. The saturation is what one would expect from the soft valve.
Dott. Marco Manfredini sent this image of the D-1 with a brass base shell. Was this use of brass by Philips unusual?
The wide glass tube envelope is 30 mm in diameter, and excluding the B4 base pins is 69 mm tall.
Reference: 3002. Type D-1 was first introduced in 1920.