BTW if this has been talked about B4 and if this mod is old news I do apologize 
, but I'm just so excited about my amps tone. I built this amp about one year ago. Everything is metroamp parts with the exception fo the chassis and the output transformer, which is the Weber 50watt Headroom.Although, the amp stock sounded great, it just wasn't the sound I was looking for. I've always loved the JCM800 2204, but felt the low input was lacking So, I decided to do the following....
I wired one set of inputs like an 800 and went with preamp volume and master volume. The other pair of inputs were disconnected
Went split cathode on V1 .68/2.7k and 6.8K
Plexi tone stack 33K/500PF
470K mixers with no cap
added a .68uf cap accross the 820 resistor on V2
added a rich mod and .022 coupling caps
instead of the 800 470K/500pf from the inputs to the preamp I went with 68K.
I kept KT66's in the power section w/ a GZ34 rect tube. Its can of bascically an 800 preamp section with a JTM45 power section.
The filtering is the same except for the 16uf axial electrolytic on the board, I changed that to 40uf.
This gave me a low input with increadible cleans with a nice gain structure as you turn up the preamp. This is also is amazing with pedals in fron of it.
The high gain channel has amazing distortion.
I had the chance to play my modded amp next to my friend JCM 800 2204. I honestly thought the 800 would sound better but was blown away at how much more organic my modded amp sounded. My friend who owns the 800 even commented that to his ears, his 800 sounded solid state to my modded JTM.
I think I have found my perfect amp.
I will try to post some clips this weekend.