This article will discuss Mercury tube testers. The Mercury Electronics Corporation of Mineola NY produced a number of tube testers in the 1960s. All models are small, portable, and lightweight. Popular models include 990, 1000 / 2000, 1100, 1100A, 1100C, 1101. Models and comments will be added as I find time. Electrical voltages are present; repairs should only be attempted by a qualified technician.