The 7S7 triode heptode was designed for frequency changer use in radio receivers. This exhibit also carries the Type designation of X81(M). The X81 is normally enclosed in an aluminium can.
The 7S7 was also made for mobile use with 12 Volt vehicle batteries for the heater, in this case the valve was called the 14S7.
The grids extend above and below the anode.
The wire support seen on the left is the connection to the triode anode.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B base pins, is 56 mm tall.
References: Data-sheet & 1040. Type 7S7 was first introduced in 1948. See also1948 adverts.
