The 6L6G is is a larger more powerful audio beam tetrode than the 6V6 receiver type. This was used for audio amplifiers and modulators for small Amplitude Modulated transmitters.
The end wall of the anode. The flanges are in the centre of the working face and thus positioned to radiate heat from where it is being generated. The GE logo is on the base.
The lower mica looking at the anode face on. The copper supports of the control grid extend outside both top and bottom micas and have heat radiating fins at either end. Success of the 6L6 depended on keeping the control grid below the temperature where it would emit secondary electrons. The bright beam forming plates can be seen either side and curve round the screen grid supports.
The classic envelope is 51 mm in diameter and, excluding the IO base pins, is 111 mm tall.
References: Data-sheet, 1040 & 1043. Type 6L6G was first introduced in 1936.