Randall RM20C

Randall RM20B

Tube config

Power valves: 2 x EL84s (Sovtek)

Preamp valves: 3 x electro-harmonix 12AX7EH - www.amplifiedparts.com/products/T-12AX7EH

Ultra module: 2 x 12AX7s (JJ) - www.amplifiedparts.com/products/T-12AX7-S-JJ

Randall MTS Ultra module JJ tubes


Celestion G12M greenback


Here are some possibilities:

Module tube choices

Warning! The tube in the V2 position is used by the module as a cathode follower.  This tube is subjected to high voltages that not all 12AX7 tubes can handle.  It is not recommended to use anything manufactured by New Sensor (ie: Tungsol and Mullard reissue, EH, Sovtek) in this position.

Related articles:

Randall RM80C


Randall MTS Recto Module

These were Randall's first attempt at a Mesa Boogie Rectifier module.  There have been a number of variants since the original Recto module, each called something different:

Randall MTS Ultra Module


Randall RM20 master volume mod

Warning! There are lethal voltages inside your RM20.  If you don't know what you are doing, then get a qualified amp tech to make these mods.

Randall MTS Brahma module

Randall described the module as follows:

Randall MTS Treadplate module

This is basically a later version of the Recto module with a few component changes.  Here's a summary of value differences.