The 6N7 is by no means a general-purpose double triode since it has a powerful heater and a common cathode. It is designed to operate in push-pull Class B2 with zero grid bias or quiescent push-pull. The anode to anode load is given as 8,000 Ohm.
It is specifically an audio power valve capable of 10 W on its own or 20 W as a parallel push-pull pair.
The 6N7 was made by RCA, the originator of the metal envelope valve.
The envelope is sealed with a hard glass foot and the lead-out wires are soldered into the IO base, also an RCA introduction.
The thin metal tube envelope is 24 mm in diameter and, excluding the IO base pins is 66 mm tall.
References: Datasheet, 3002 & 1040. Type 6N7 was first introduced in 1936.