Mektronic Engg. Co. Offers Test Tube Warmer with Temperature Display. Mektronic Engg. Co also manufactures various types of medical and surgical instruments. The Test Tube Warmer with Temperature Display has three aluminum blocks to warm four to six tubes each. The Test Tube and Petri Dish Warmer has auto cut-off on set temperature. The Test Tube and Petri Dish Warmer has PID controlled of heating. The Test Tube and Petri Dish Warmer has Voltage 230V of A. C.