The RAF Type C was developed at the end of WWI, it is a hard vacuum triode designed for RF or AF amplification and is fitted to an Inter-services type 1 base I/S1. In the same style of envelope and base and made at the same time was the RAF Type D, a soft valve used at a detector in equipment that used the Type C as amplifiers.
The filament is a straight tungsten wire and in this exhibit is is broken. The top connection to the filament is by a spring attached to a support sealed into the pinch. The wire passes through the pinch to the base and thence via an external metal strip to the top contact. The lower end of the filament connects to the other end contact. The grid and anode are brought out to side contacts.
The RAF Type C went into production in September 1918. This type of valve was made by GEC and Edison Swan. This exhibit was made by Royal Ediswan.
The grid connection is marked with a G and the anode with an A. Between the letters on the base is the word Top, so this valve is upside down.
The external filament connection and at the extreme right the word Top.
The broken filament looks to be a clean break from shock rather than a point that has melted in use.
The identification is clear in this image but normally is hard to see. The RAF is close to the base (sorry top).
The moulded filament connection.
The grid helix is offset within the anode cylinder and this movement was probably caused by the impact that broke the filament. The thin wire wraps round the support and the coils of the helix to keep the helix in position.
The wide glass tube envelope is 25 mm in diameter, and including the base pins is 82 mm tall.
References: 1003 & 1047. Type C was first introduced in 1918.