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 dark rectangle is where the metal has been pressed forward so that only a small area forms the working anode surface.
The side view.
The actual construction can not be determined from the external appearance.
Thanks to Mike Tonkin for sending the Lamba Valves.
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. See also1961 adverts.
