Type 836 is an American high voltage half wave rectifier. The maximum peak inverse voltage on the anode is 5,000 Volts and the peak cathode current is 1,000 mA.
The anode pressing has a small depth. The bracing supports can be seen fixed to the lower electrode support and on to the top mica. The mica itself is an interference fit to the shoulder of the envelope.
The lower end of the anode. At the top is the support strut to the top mica and attached to that is the getter support that can be seen arching over to the top right. The lower support is ceramic.
The top of the electrodes. The filaments are in series and joined above the top mica by a stiff wire.
The classic envelope is 60 mm in diameter and, excluding the UX4 base pins, is 150 mm tall.
References: Data-sheet & 4061. Type 836 was first introduced in 1938.