The AC/VP1 is a variable μ screened pentode designed for mains radio receivers. The variable μ characteristic enables automatic gain control of RF and IF amplifiers in superhet receivers.
This exhibit has the old style of screw top cap. As the top hat top cap design was being introduced at the time of the AC/VP1 release (1934) This must be from an early batch.
The AC/VP1 and AC/VP2 were the standard RF/IF screened pentodes in the Mazda range for AC mains radios from the mid-1930s until domestic radio manufacture was interrupted by WWII.
The two valve types were essentially identical except that the AC/VP1 has its anode connected to the top cap, as with most screen-grid valves. The AC/VP2 has the control grid (g1) connected to the top cap, as was standard for later IF pentodes.
The reverse is plain zinc screening paint.
The Bakelite skirt and screw top cap connection. The insulated cap is missing.
The classic envelope is 39 mm in diameter and, excluding the B7 base pins, is 107 mm tall.
References: Data-sheet & 1040. Type AC/VP1 was first introduced in 1934.