The CV58 is a detector diode designed to operate at microwave frequencies at a wavelength of 9 cm. Radar was the design use. The prototype was the E1273.
The central pin is the heater and the outer tube is the heater and cathode connection.
The helical insulated heater can just be seen in the cathode tube. The oxide coating is only on the flat top.
The thin glass tube envelope is 12 mm in diameter, and including the base pins is 43 mm tall.
