Sylvania Brown Base Gold Label JAN-CHS-5Y3WGTA (ruggedized 5Y3GT) Rectifier Tube
Hickok 539B is a mutual conductance (Gm) type tube tester. Tube features black ribbed- platesand a top-mounted 'halo-ring' getter construction. Minimum acceptable test value for a good tube. (Plate#1 / Plate#2).