The 25L6GT is designed for use in single ended audio stages in apparatus using a 300 mA series heater chain. As a single ended audio amplifier it can produce 4.3 Watts.
Tele King made television receivers in the USA. Clearly they bought-in valves branded for them.
The dome carries the identification and the maker was probably RCA.
An enhanced image of the dome showing the 25LS GT a little more clearly. The lettering is within an octagonal border.
The wide glass envelope is 29 mm in diameter and, excluding the IO base pins, is 68 mm tall.
References: Data-sheet, 1040 & 1043. Type 25L6GT was first introduced in 1937. See also1937 adverts.
