The EL360 is an output pentode introduced by Mullard in October 1958. The applications are: radar scanning, series regulator and pulse modulator. The ratings given are for pentode use. The data-sheet shows that for high voltage regulator and pulse modulator use the peak voltage can reach several kV.
The anode looking into the side seam which is in the centre of the working face. The high voltage rating for pulse use is the reason for the ceramic insulators.
The anode seen along the grid axis. The support rods pass between the two halves of the anode plate. The grid heat sink fins can be seen above the top mica connected to the copper grid supports.
A closer view of the top mica components.
Thanks to David Anders for the PDF.
The wide glass tube envelope is 32 mm in diameter, and excluding the base pins is 95 mm tall.
References: Data-sheet. Type EL360 was first introduced in 1958.