The 2A6 double diode triode is designed for detector and first audio stage in radio receivers. The heater voltage of 2.5 Volts is unusual in the UK. A heater voltage of 2.5V was the original (late 1920s) standard for American indirectly-heated AC mains valves. The change to a 6.3V standard came about because of the demand (in the US) for car radios in the early and mid 1930s (most US cars at that time still had 6V electrical systems). This exhibit is a much later (post-War) replacement type branded Tungsram but probably factored. 2.5-volt valves were obsolete in the US by then but remained in demand for replacement purposes, eg. in South America. The interesting thing is that such a valve should have a CV number, particularly since it was essentially a US domestic radio type.

The valve has a common cathode assembly, seen running vertically through the centre of the valve. The signal diode anodes are the bright plates seen in the centre of the envelope. Each side is insulated and forms a diode anode. The top of the electrode structure is the triode. The anode cavity is blackened.

The classic envelope is 36 mm in diameter and, excluding the UX6 base pins, is 98 mm tall.

 
Pin Connections

UX6	1	2	3	4	5	6	tc
	h	a	a(d2)	a(d1)	k	h	g1

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	2.5	0.8	250	-1.35	0.4	91k	1.1

Thanks to Frank Philipse for supplying the above datasheet

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