This valve is marked both CV5809 and E810F. Mullard describe the E810F as a special quality high slope pentode designed for use in industrial equipment where stability of characteristics and long life are required. It is a wideband RF device, but no frequency range is given. From the information available it appears that 40 - 100 MHz is a probable upper value. Oscilloscope amplifiers and other measuring instruments are likely candidates for this valve. We believe that this valve dates from the 1960s.
The envelope carries the later Mullard logo and was made by the Parent company Philips in Holland.
As a well screened valve, little of the inner structure is visible. The top mica looks to be double thickness.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 45 mm tall.
References: Data-sheet & 1040. Type CV5809 was first introduced in 1958. See also1958 adverts.