Want a cleaner front end and the earlier breakup of the JJ EL844's? This is our Low Output SRV Option Retube Kit for the Dr. Z Maz 18 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 standard JJ ECC81 to replace the 12AT7, a 5751 for V1 along with three JJ ECC83S's with one being current balanced for the phase inverter in V5.