THD Electronics YJUNI Yellow Jacket for UniValve, Single, w/Tube Yellow Jackets are a type of specialized adapter which permit the use of EL84/6BQ5 power tubes in place of 6V6, 6L6 and EL34 types. Incliude one Yellow Jacket Converter and one EL84 power tube. Standard type for THD UniValve and Bi-Valve-30 amplifiers. Reduces the power by about 50% and converts the amplifier to Triode operation. Gives smoother overdrive, more sustain, richer mid-range harmonic content and greated touch-sensitivity, all at a lower volume. Hand-built in Seattle, WA.