THD Electronics YJ20S Yellow Jacket for 6V6 Amps, Single, w/Tube Yellow Jackets are a type of specialized adapter which permit the use of EL84/6BQ5 power tubes in place of 6V6 types, and converts any amp to Class-A operation. Incliude one Yellow Jacket Converter and one EL84 power tube. Standard type for most 6V6 amps. Does not appreciably reduce the power of the amplifier. Gives smoother overdrive, more sustain, richer mid-range harmonic content and greated touch-sensitivity. Hand-built in Seattle, WA.