Prior to 2010, most television sets used cathode ray tubes to display the picture. These tubes were essentially electron guns that shot electrons at a phosphor-coated screen, which would light up to create the image. The tubes were designed to last for about 1,000 hours of use, after which they could be replaced for $3-$4. From the late 1920s until the early 1970s, many department stores, drugs stores, and grocery stores had self-service tube-vending displays. They typically consisted of a tube-tester atop a locked cabinet of tubes, with a flip chart of instructions. One would remove the tubes from the TV set, take them to the store, and test them. If the tubes were defective, new ones could be purchased from the cabinet. Tube were installed in sockets and were easily replaceable with guidance from a diagram showing where to replace each tube. If testing showed all tubes to be working, the next step was to call a TV repairman.
