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 also 6BE6 that is identical apart from having a 6.3 Volt heater.

The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 47 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type 12BE6 was first introduced^¶ in 1950.

 
Pin Connections

B7G	1	2	3	4	5	6	7
	g1	k	h	h	a	g2,g4	g3

 
Absolute Maximum Operating Conditions^¶

Heptode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Vosc
	12.6	0.15	250	100	-1.5	3	7.1	1M	0.475	10

Thanks to Frank Philipse for supplying the above PDF datasheet