Full details for the 3CX100A5 can be found on the attached data sheet.
It is the same size as the 2C39A with the only visual difference being ceramic replacing the glass.
Ceramic insulation would suggest a higher power than the 2C39A's 20 Watts of up to 2400 MHZ and the data sheet confirms this.
Here is another example but this time within the connectors. The grid line is at the top and the anode plate below.
The Note the US Army lettering. The anode connection is a ring of silver plated fingers.
The anode finger stock is on the right. The silver plated tube contains the fingers for connecting to the heater, heater/cathode and control grid in ever increasing diameters. The valve simply pushes into the top of the line.
The anode plate removed from the valve.
The planar envelope is 32 mm in diameter and, is 69 mm tall.