The 6L6G it 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 lettering on the base cap has bother the commercial Type designation and the USA government procurement code of VT-115A.
The National Union stylised lettering and Made in USA.
The end of the beam plate is visible as a bright structure inside the anode. The control grid supports are copper rods. On the glass can be seen the etched octagon containing the Type designation.
This close-up shows the geometry with the sides of the open box beam plates covering the ends of the screen grid.
The stitched anode and a clear image of the cathode with flat sides and rounded ends. The anode has a central flange for added heat removal.
The tops of the control grid supports have small fins mounted on them to assist with cooling the grid to reduce the possibility for the emission of secondary electrons.
The top mica showing both the shape of the cathode tube and the cooling fin on the control grid supports.
The classic envelope is 51 mm in diameter and, excluding the IO base pins, is 115 mm tall.
References: Data-sheet, 1040 & 1043. Type 6L6G was first introduced in 1936. See also1936 adverts.
