The VT-117A is the American Government code for the commercial 6SK7GT variable μ pentode. Design use is for RF and IF amplifiers in superhet receivers. The gain of the device being controlled by a negative voltage derived from rectifying the final IF signal. In this way strong signals do not overload the receive chain because the various controlled stages have their gain reduced.
The 'S' denotes a single ended design whereas the 6K7GT has the control grid connection made at the top cap. Here the control grid pin is between the suppressor grid and the cathode - all close to ground potential.
The anode lead is screened from the rest. The commercial Type designation is printed on the glass.
The other anode plate is also screened from the central connections.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 70 mm tall.
References: Data-sheet & 1040. Type VT-117A was first introduced in 1940. See also1940 adverts.
