Want all the gain you can get and the earlier breakup of the JJ EL844's? This is our Low Output High Gain Option Retube Kit for the Dr. Z Prescription ES Heads and Combo Amps. It contains a matched quad of JJ EL844's for power to drop the overall output a couple decibels, a JJ GZ34 rectifier tube, an EF806 for V2 along with two handpicked High Gain JJ ECC83S's with one being current balanced for the phase inverter in V3.