Want all the gain you can get? This is our High Gain Option Retube kit for the Dr. Z Maz 18 Heads and Combo Amps. It includes a matched pair of the JJ EL84's for power, a JJ GZ34, one JJ ECC81 to replace the 12AT7, two handpicked High Gain ECC83S's for V1 and V2 along with two ECC83S's with one being current balanced for the phase inverter in V5. Mike recommends a JJ gt #6 for power but since we have 30 different grades of the JJ EL84's and we know where the bias point is on these amps, just let us know in the comments section if you're looking for an early breakup, a moderate breakup or a later breakup for more headroom in which case we will choose the coolest grades we have available for the power tubes.