Low voltage color tube gun assembly with periodic focusing

One type of color tube, often referred to as the post acceleration color tube, requires a gun of unique design. The gun operates at relatively low voltages of 5,000 to 7,000 volts as compared with 20,000 to 30,000 volts in other types of color tubes. The tri-color gun assembly described consists of three individual guns arranged in a plane. This limits the inside diameter of the electrodes to 0.358 inches as compared with half an inch or more in conventional guns. The individual guns are either triodes or tetrodes with periodic focusing. In spite of the above mentioned restrictions the spot size is about 0.398 inches at 300 microamperes screen current per gun and 7,000 volts anode voltage. The depth of focus is very satisfactory because of small beam diameter. As a further step in this development, high voltage high resolution guns with half inch diameter electrodes were built using the same multi-focusing lens principle.