The 6G6G audio output pentode was designed for radio receiver use. The designation VT-198A is on the box and it is marked for the US Army Signal Corps.
The whole point of type 6G6 is economy of heater and HT consumption where only modest audio output is required. As such, it was a good choice for driving the internal speakers of communications receivers, including types used by the military. The 'VT' designation is here part of the WWII US Government sequence (comparable to our CV sequence) and stands for 'vacuum tube'. Unlike the (entirely independent) British RAF 'VT' sequence, a transmitting application is not necessarily implied.
The identification is printed in an octagon on the glass and again on the base cap.
The glass lettering - feint but just readable.
The Ken-Rad name and Made in USA.
The mica sheets hold the electrodes firmly in the shoulder of the envelope. Here all three wire grids can be seen together with the white coating on the cathode.
The classic envelope is 38 mm in diameter and, excluding the IO base pins the valve is 88 mm tall.
References: Data-sheet & 1040. Type 6G6G was first introduced in 1937. See also1937 adverts.
