A 5 inch version of the new Ferranti high-resolution cathode ray tubes.
Electrostatic focusing at near-cathode potential and low-power magnetic focusing techniques are combined in a new series of high-resolution cathode ray tubes developed by Ferranti of Hollinwood, Lanes. Tubes of this series which are available at present, Types 5E/12 and 3C/12, achieve a minimum spatial frequency response resolution of 150 cycles per centimetre. (Other types in development are capable of a spatial frequency response of 200 c/cm). Large electrostatic lenses are used, which, when operated at cathode potential act as the primary lens and only small degrees of spherical aberration and astigmatism are produced. Astigmatism correction coils mounted on the neck of the tube reduces this latter effect. EHT variations of up to 2% do not appreciably deteriorate focus. A small, low-power electromagnetic lens is employed as a secondary correction lens in the tube.
The maximum anode voltage is 20 kV while that of the electrostatic lens or second anode is 500V. The nominal grid voltage for usual cut-off is Va / 300. The tubes have 6.3V heaters and the maximum resistance of the dynamic focus coils is 50Ω.
Different phosphors are available and screen thicknesses are optimized for either 7kV or 15kV operation.