The 12H6 is the smallest metal valve we have seen. In the metal envelope, and sharing a common heater connection are two separate signal diodes. Such a device could be used in FM demodulation and a host of other low level rectification. We do not have details of the original design application beyond military communications. An American television textbook of 1950 uses these valves extensively as level clamping diodes.

The thin metal tube envelope is 25 mm in diameter and, excluding the IO base pins, is 28 mm tall.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a(2)	k(2)	a(1)	-	h	k(1)

 
Absolute Maximum Operating Conditions

Diode	Vh	Ah	Va	mAa
	12.6	0.10	117	8

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 02 December 2007 {find valves by name}