The PL36 was designed for service as a line timebase output valve in television receivers and is designed for series heater chain use. It has a 6.3 Volt parallel heater version the EL36. This is the Tungsram implementation of the design and the discolouration within the glass speaks of a previous hard service life.
The maximum positive peak voltage on the anode is 7 kV and the screen dissipation is up to 5 W.
The central seam of the anode and above the top mica the control grid heat sink fins can be seen.
Looking along the grid axis.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 94 mm tall.
References: Datasheet, 3002, 1040 & 1043. Type PL36 was first introduced in 1955.