In the three-electrode tube, the "Pliotron", the grid is shown at G, the filament at F - which is supported by a glass frame - and the plate or anode at A. The grid consist of a number of turns of tungsten wire .01 millimetre in diameter, spaced to include 100 turns to the centimetre. The filament is mounted inside the grid. The plates or anodes on either side of the filament consist of tungsten wire wound zigzag in the manner shown.
A large "Pliotron" which may be termed a "power" bulb. A tube of these dimensions may be employed to generate several watts of radio frequency alternating current from a source of direct current. Hundreds of bulbs may be connected in parallel for the production of radio frequency currents at very large powers.

From the book 'Vacuum Tubes in Wireless Communication' by Elmer E. Bucher. Published in 1919