The 12AT6 is a double diode triode for superhet receiver applications. It is of medium impedance and very low current. Type 6AT6 differs only in having a 6.3 Volt heater.
The distinctive electrode configuration, the central triode with the pair of long diode anodes either side. The active area of the diodes is above the top mica.
Here one of the diode anodes can be seen as two thin parallel sheets. The bridge between them is the active anode.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
References: Data-sheet & 1040. Type 12AT6 was first introduced in 1946. See also1946 adverts.
