Now that I think about it, the standard design of a Trainwreck Express leaves
 half of a 12AX7 unused. 
 
    When the early cloners here complained about their amps being too 
harsh I figured that a good use of that extra triode would be a switchable
 cathode follower as in the Mesa Boogie Maverick (still my favorite amp
 that you can find at GC, etc.). The rhythm channel has a fat/bright(?) switch that toggles the connection to the BF style tone stack from the anode of V1a to the cathode of V1b. I figured that it would be a cool addition to the basic Express design...


Dave: Would that work on any 2 channel 1 tone stack amp Steve?
 
    The Maverick rhythm channel uses a tone stack like a BF Fender, 
at least when the Bright mode is selected, with the input going to a single
 stage which feeds the tone stack from the anode.
 
    When the Fat mode is engaged there is a cathode follower inserted 
between the first stage and the tone stack (which is then driven by the
 cathode). The CF does not add gain to the preamp but it has a lower
 impedance so perhaps it drives the tone stack more efficiently, thus
 boosting the low frequencies.
 
    Now the traditional Marshall style tone stack is already driven by a CF
 so one thing to consider is to add another stage after the CF which would
 drive the tone stack from its anode. In this case the added stage would 
(or could) add gain to the signal. FWIW that is essentially what I did with
 my Peavey Classic 50 when I replaced the stock OD stages with a 5F6A 
dc coupled pair w/ cathode follower; the CF drives a gain stage which
 feeds the Marshall style tone stack from its anode.
 
Steve Ahola