nice, restored Hickok 539A the Caddilac of mutual conductance lab-grade tube testers. If you are looking at this, you know what it is and how nice it is! This one has been nicely cleaned up with most of the tube sockets replaced with brand new sockets (4, 5, 6, 7, 9, 7, 8, octal) and the others replaced with very good but used sockets. All resistors checked and replaced were needed, and caps replaced as well. Calibrated, this comes with a copy of the users manual, and has been rewired for safe operation with a modern 3-prong AC plug. Please feel free to ask questions...