The 6BN8 is a double diode high μ triode with a controlled warm-up time of 11 seconds. It is pin compatible with the 6BJ8 but has different ratings.
Controlled warm-up is usually for valves within a series heater chain and this valve was probably used within television receivers.
The layout has three separate sections with the triode in the centre. There is no common connection between the three sections.
The anodes are all stitched together and the triode has copper grid supports. The triode cathode has flat sides whilst the diode cathodes are round tubes.
One diode face view.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 59 mm tall.
Reference: Data-sheet. Type 6BN8 was first introduced in 1958. See also1958 adverts.
