The 5814A is a medium μ double triode closely related to the 12AU7 but made to a mil spec especially for electro insulation.

Current information gives the valve as now being made by Philips ECG in the USA.

The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 47 mm tall.

Reference: Datasheet. Type 5814A was first introduced^¶ in 1954.

 
Pin Connections

B9A	1	2	3	4	5	6	7	8	9
	a(2)	g1(2)	k(2)	h	h	a(1)	g1(1)	k(1)	hct

 
Absolute Maximum Operating Conditions^¶

Triode	Vh	Ah	Va	Vg	mAa	gm
	6.3	0.3	250	-8.5	10.5	2.2

Thanks to Frank Philipse for supplying the above PDF datasheet