The EF86 is the standard early stage audio pre-amplifier valve. This exhibit was made by Mullard who designed the EF86. It was first used in their 5-10 amplifier from 1954. This particular valve was made by Philips (the Mullard parent company) in Holland.
Mullard describe the EF86 as 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 screening mesh and below the bottom mica addditional screening.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
Reference: Datasheet & 1040. Type EF86 was first introduced in 1953.