The 5963 is a special quality double triode introduced in 1954 for use in computer and frequency divider circuits where the valve will spend much of its time cut off.
The centre tapped heater allows for the sections to be run in series (connect to pins 4 and 5 and run at 12.6 V) or parallel (connect pins 4 and 5 together and feed at that junction and pin 9 with 6.3 V).
An oblique image of one section. The anode is carbonised to improve heat dissipation and ribbed to obtain a rigid anode from thin sheet material.
The pair of triodes and the HP logo on this RCA valve.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 49 mm tall.
References: Datasheet, 3002 & 1040. Type 5963 was first introduced in 1954.