Type 6J7 was originally designed as a detector, but the linear characteristic and good internal shielding (cf. 6Q7GT) made it a natural choice for audio. It was for twenty years the international standard valve for audio amplifier input stages and audio systems.
The Philips-Mullard type EF37A, for many years the standard British low-noise audio pentode, is really a 6J7G under another name. The predecessor valve was the Type 57 and the characteristics are the same.
The maker's name and Made in USA.
The thin metal tube envelope is 25 mm in diameter, and excluding the IO base pins, is 63 mm tall.
References: Datasheet, 1040 & 1043. Type 6J7 was first introduced in 1936.