The HF-100 is a transmitting triode with an anode made of graphite that can dissipate up to 75 Watts. The maximum operating frequency at full ratings is 30 MHz - hence the HF tag. In Class C with 1.500 Volts on the anode the putput is of the order of 170 Watts from a single valve.
The valve is also specified for use as a Class B audio amplifier or modulator. With 1,750 Volts on the anodes the maximum audio power is 350 Watts - but not hi-fi.
The control grid is brought out to a large side cap.
The grid winding within the graphite anode. The filament tension springs are set into a ceramic support that is joined to a metal box section to the lower ceramic support and thence to a collar around the pinch stem.
At the lower ends of the filament tension springs can be seen the top loops of the thoriated tungsten filament.
The pinch stem with the collar holding the box supports rigidly in place.
The substantial tape passing from grid to side cap.
The ceramic base cap and UX4 pins. The data-sheet seems to show the filament connected to the smaller pins (2 and3), however, on test the filament is between 1 and 4 as one would expect in a UX4 base.
The wide glass tube envelope is 51 mm in diameter, and excluding the UX4 base pins is 183 mm tall.
References: Data-sheet, 1040 & 1043. Type HF100 was first introduced in 1947.