This Mullard PC97 was made in Great Britain and is an RF amplifier triode. It has a high mutual conductance and could be used as a signal pre-amplifier. Its design use would be in domestic television receivers. The PDF carries a date of 1962 and the logo on the glass indicates that this exhibit was made no earlier than 1970.
The PC97 is a frame grid triode that in addition to a very high mutual conductance of 13.00 mA/V has an unusually low grid to anode capacitance of about 0.5 pF. This low capacitance is obtained by using a special shield between grid and anode in conjunction with a shaped anode. Because of this shield that is in place except in the active cathode to anode region these valves are also known as Beam Triodes. An additional benefit is that the neutralising capacitor can be connected to ground on one side. The PC95 also uses this construction technique.
The actual triode is small compared with the 20 mm diameter glass tube.
The tutorial referenced above gives a diagram of the construction. The bright metal in the centre of this image is the screen.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 47 mm tall.
References: Data-sheet & 1040. Type PC97 was first introduced in 1961.