Years ago we did a lot of research into tubes that work well for harp players. What we found is that unlike amps used for guitar, a harp amp likes a phase inverter tube that is NOT balanced. So this kit includes a matched pair of the JJ EL844's for reduced power, a standard ECC81 for V1, an ECC83S for V2 and an ECC832 for V3. This gets you less feedback and an earlier breakup while accentuating the unique harmonics that make Harp sound so cool.