The 12BE6 is a heptode or pentagrid valve. The heptode is classically used as a frequency changer in a superhet receiver. Radio and Television both use the superhet principle. To change frequency the incoming signal is mixed with a local oscillator. The electron stream is effectively switched on and off by the oscillator. In practice the process is one of producing sum and difference frequencies rather than just mixing of two signals.
To prevent the oscillator and the signal interfering in unplanned ways a screening grid keeps the circuits apart.
See also6BE6 that is identical apart from having a 6.3 Volt heater.
The outer grid wires extend beyond the small anode plates. The strap joins the two halves together and the whole anode is pressed from a single strip.
In this example it is difficult to see both screening grids and it looks more like a pentode.
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 12BE6 was first introduced in 1946. See also1946 adverts.
