The EICO Model 666 Dynamic Conductance Tube & Transistor Tester is one of the first thoroughly practical service instruments able to test both tubes and transistors. Among its advantages are rapid and simple operation, close simulation of actual tube operating conditions, and unexcelled thoroughness and accuracy of test. The outstanding mechanical design and layout, coupled with components carefully selected for ruggedness, makes the Model 666 extremely well-suited for the hard usage of daily service work. All components of the Model 666 tube tester are assembled to the heavy-gauge aluminum front panel, which is in turn top-mounted by 14 screws to flanges on all four sides of the steel case. A detachable steel cover is mounted to the back of the case with separable hinges so that the cover may easily be removed for use of the instrument as a counter-top model or replaced to convert it back to a portable instrument. There are ten different tube sockets on the panel to accommodate any receiving tube, old or new, and whether it be standard size, miniature, or sub-miniature. In addition, pi lot and Christmas tree lamps can be checked rapidly using the center of the large 7-pin socket. A special transistor socket accommodates both n-p-n and p-n-p transistors. To protect against damage due to current overload, a type 3AG 1 ampere fuse is connected in series with the primary of the power transformer.