The 6AL5 is a double signal diode. Mullard separate rectifier diodes and signal diodes in their naming convention and the EB91 would be their own version of this valve. It is interesting that Mullard have used another manufacturers type designation.

The two valves are completely separate flat structures separated by a plate screen. This clearly shows the signal usage, where it is important to keep RF isolation.

These double diodes were designed for sound and vision detection in 405 line televisions. Additionally they are recommended for limiting and DC restoration, again part of a TV receiver functionality.

The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 37 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type 6AL5 was first introduced^¶ in 1945.

 
Pin Connections

B7G	1	2	3	4	5	6	7
	k(1)	a(2)	h	h	k(2)	s	a(1)

 
Absolute Maximum Operating Conditions^¶

Diode	Vh	Ah	Va	mAa
	6.3	0.3	150	9

Thanks to Frank Philipse for supplying the above PDF datasheet

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