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 5000 to 7000 volts as compared with 20,000 to 30,000 volts in other types of color tubes. The tricolor gun assembly described consists of three individual guns arranged in a plane. This limits the inside diameter of the electrodes to 0.358 inch 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 0.038 inch at 300 microamperes screen current per gun and 7000 volts anode voltage. The depth of focus is very satisfactory because of small beam diameter.