THD Electronics YJ20D Yellow Jacket for 6V6 Amps, Duet, w/Tubes 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 two Yellow Jacket Converters and two EL84 power tubes. 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.