Want a cleaner front end to go with the earlier breakup of the JJ EL844's? This is our Low Output SRV Option Retube Kit for the Dr. Z Maz 18 Non-Reverb Heads and Combo Amps. It contains a matched pair of JJ EL844's for power to drop the overall output a couple decibels, a JJ GZ34 rectifier tube, a JJ 5751 for V1 along with two JJ ECC83S's with one being current balanced for the phase inverter in V3.