Type 6N7 is by no means a general-purpose double triode since it has two powerful heaters, a common cathode, and is designed to operate in push-pull Class B2 with zero grid bias. The anode to anode load is given as 8,000 Ohm.
It is specifically an audio power valve capable of 10W per pair. Provided plenty of HT voltage is available it can also be used, with both halves connected in parallel, Class A1, as a power driver for another 6N7.
Type 6A6 is the same valve but on a UX7 base.
The wide glass tube envelope is 27 mm in diameter, and excluding the IO base pins, is 65 mm tall.
References: Datasheet, 1040 & 1043. Type 6N7GT was first introduced in 1936.