Miniature wire ended valves, like the 505AX were developed in WW2 for military use, and for hearing aids.

This valve could have found use as the first stage of a hearing aid.

The thin glass tube envelope is an oval tube 9 x 7 mm, and excluding the wire leads is 30 mm tall.

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	0.625	0.03	45	45	-1.25	0.2	0.08	2M	0.15

This exhibit was last updated on 04 July 2007