The 12SQ7GT/G is a double diode triode with heaters designed to operate from the 12.6 volts available in a vehicle. The diodes are for AM signal detection and AGC detection whilst the triode section is for first audio amplification. This is typical for a valve used in a radio superhet receiver.
Apart from the 12.6 volt heaters the valve characteristics are equal to the 6SQ7 the GT is for glass tubular construction.
The Sylvania name on the metal base skirt. Above the gettering is the triode section.
Here the construction is clear. The common cathode passes through the diode screening box before reaching the triode. The diode anodes are rods that are visible in the pinch either side of the heater supports.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 68 mm tall.
References: Data-sheet, 1040 & 1043. Type 12SQ7GT/G was first introduced in 1939. See also1939 adverts.
