The 1J6G is an audio output valve designed for battery broadcast receivers. The two sections operate as a Class B push pull pair. Class B sufferers from crossover distortion where one valve goes into conduction and the other is driven to cut-off but for a given HT consumption gives greater output power and thus more volume. AM broadcast radio was never a hi-fi transmission medium.
The type 19 has the same operating characteristics but different heating. The valve is marked 'Made in USA' and is clearly not a European design.
The mica is an interference fit into the bulb to give mechanical rigidity. The low power of the valve allows for the anode sections to be left bright. The ridges pressed into the thin metal gives strength for minimal material used.
The stitches holding the two halves of the anode together are clearly seen. Less clear due to the distortion of the bulb glass is the filament tension spring, the inverted v of the filament and the fact that the filament is oxide coated for maximum emission at minimum heating power.
The classic envelope is 38 mm in diameter, and excluding the IO base pins is 87 mm tall.
References: Datasheet, 3002 & 1043. Type 1J6G was first introduced in 1936.