THD Yellow Jacket Converter YJS Triode with EL84 Tube Single Can be used in place of 6V6, 6L6, EL34, 7027 6550 (under 520 volts) and 7591 typesWork in any amplifier that takes these tube types, as long as the plate voltage is under 520 VDCRevitalizes the sound of your ampAlso work in tube Hi-Fi equipment How do they work?They give you simple Class-A operation from any amp Yellow Jacket Converters not only rearrange the pin locations of the tubes, but also provide the necessary current limiting on the screens and cathode as well as blocking the amplifier's grid bias voltage, while configuring the EL84 in a Class-A, Self-adjusiting cathode-bias circuit In other words, there are no adjustments to make and no modifications necesary, you simply plug the Yellow Jackets into the amp's output tube sockets, (in cathode-bias amplifiers) screw the ground wires under one of the output tube socket mounting screws, plug the provided EL84's into the Yellow Jackets, turn on the amp and play How will they change my amplifier?It's like getting a whole new amplifier! In Champ and Deluxe type amplifiers, the Yellow Jackets output is smooth, strong and more even than with the stock 6V6s