The E83F Mullard pentode is a special quality version of the EF83.
The valve was designed for class A audio amplification in telephone equipment where long life was very important. The audio output was 0.87 Watts and the maximum anode dissipation was 2.1 W.
The writing says Special Quality. Inside the screen can just be seen the open helix of the suppressor grid and the two parts of the anode.
The black anode inside the mesh screen. The mica sheets are quite thick but no double mica is used. Here the SQ is for long life not vibration resistance.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 60 mm tall.
Reference: Data-sheet & Philips Pocketbook for Hams 1962. Type E83F was first introduced in 1958. See also1958 adverts.
