The EF86 is the standard early stage audio pre-amplifier valve.
The EF86 is a low noise pentode intended for use as a RC coupled AF voltage amplifier, particularly in the early stages of high gain audio amplifiers, microphone pre-amplifiers and magnetic tape recorders.
The screen is dimpled and not perforated.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
Reference: Datasheet & 1040. Type EF86 was first introduced in 1953.