The 6SK7GT is a 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 printed commercial Type designation on the envelope contained within an octagonal border. The VT number is VT-117A whereas the VT-117 is the original metal valve version.
The National Union name and Made in USA.
Looking through the notch in the outer cylindrical screen the three wire grids can be seen.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 70 mm tall.
References: Data-sheet & 1040. Type 6SK7GT was first introduced in 1940. See also1940 adverts.
