The YL1000 is a quick heating directly heated VHF pentode for use as a power amplifier of frequency multiplier in portable or mobile equipment. As a power amplifier it would be operated as Class C for FM equipment. It will heat to 70% of maximum output in less than 0.5 seconds.
The anode is shaped to form two wide bands around the ends of the grids and a flat sheet in front of the grids.
The glass has a mottled surface that obscures the fine internal details.
The multi-stranded filament is retained by top springs to maintain tension. If the filament sagged when hot the distance to the control grid would vary and alter the operating characteristics.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 59 mm tall.
Reference: Datasheet. Type YL1000 was first introduced in 1964.