The EB91 is a double signal diode. These diodes were designed for vision and sound detection. Additionally they are recommended for limiting and DC restoration.
This is an import as the valve is labelled Foreign.
The glass is discoloured between the mica discs. This could be a coating to reduce the effects of electron bombardment on the glass, or if uncoated it is the effects of such bombardment.
The typical construction of two diode sections and a central screen.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 37 mm tall.
References: Data-sheet & 1040. Type EB91 was first introduced in 1949. See also1949 adverts.
