The EF86/Z729 is the standard early stage audio pre-amplifier valve that replaced the EF37A in the early 1950's.
The Z729 is 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 assembly is rigid to eliminate microphony and the heater is a twisted pair to reduce any external magnetic field and thus hum pick-up.
The GEC brand label.
The outer screen obscures the inner pentode structure. EF86 has an image that shows the inner grids.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
Reference: Data-sheet & 1040. Type Z729 was first introduced in 1959. See also1959 adverts.
