One of the main reasons I did some modding is because I chose the wrong tubes for this head. The other is I think i biased it to hot (%70). Plate minus cathode readings. I installed and biased a set of 6ca7EH. I really like this variant of el34 but, boy are they bright. They would probably sound best in a vintage amp that needs all new caps. The P.I. tube I chose the Reissue Mullard 12ax7 because it just suited my ear the best.
I liked the results except I couldn't get enough fizz out. I Should have just swapped tubes or spent major money replacing all my speakers but, I didn't because of a tight budget. So, I started to searching the web for, "Marshall anti-fizz mod", etc, etc. I came across a mod to swap the P.I. coupling cap for a higher value. While this cap in early Fender/Marshall designs isn't for tone sculpting, I did it any way. I settled on 100p because that is what the value of the JVM410HJS cap is on the drawing. Thanks Santiago. I didn't like the result though, I used the wrong type of cap. I should have went with a regular ceramic, instead I used a double space blue one. Definitely not a tone cap of my liking.
Being a compete novice to tube amp modding, I didn't want to pull apart the chassis again for one cap. So I kept looking for more mods. I found another mod where you run (1)120p cap in parallel with the P.I. resisters on the push and pull sides. Easy mod, no pulling the board again. I used the orange drop style caps. Wish I could find those in 100p 500 volt for the coupling cap because these sound awesome. These caps are problematic though when you bend them, if you crack the insulation as I did when installing them, humidity,etc gets inside them and can make the cap fail prematurely. This mod essentially creates a notch filter of about -3db (I think) or half volume of the notched frequency. I don't know how to do the math to figure out which frequency I cut but, this mod did the trick for the most part.
Still not satisfied, I put a 5hy choke in there. Simply put, this amp doesn't need it. It altered the sound some for the liking and disliking. The design of the amp and spec. of the transformer without the mod is more than sufficient. The only thing I am itching to try is a different O.T. Even though I believe it is good quality transformer, ones designed just like the transformers in vintage JCM 800's would be totally killer. Or an upgraded version of the JVM410 transformer so I can run 8 and 4 ohms cabinets simultaneously without a ohm mismatch, that would be killer. I believe each set of speaker connections in a JVM410 has a dedicated ground for each speaker connection. Normal Marshall amps share a ground that is lifted or not, depending which speaker output you are using.
I need to remove the the blue 100p cap, it is giving me a sizzling bacon kind of treble sound sometimes in the dirt channels. Unless that is the P.I. resister-cap mod because the push and pull sides are cutting different frequencies. This amp still sounds near perfect to me though. If there needs to be any corrections, etc because of of me being a novice, please do so. I am here to learn and meet awesome people. So far, mission accomplished.
With all of this said.....on to the sound clips.
I purposely stayed away from going in to to much detail about the mods as to discourage others from going mod crazy on a perfectly good head.
This amp has so many good sounds though.
Seriously though,Thanks. I could've made it sound better but I wanted it to sound like I was standing next to the amp. I didn't want people saying " I used the settings and it didn't sound like yours at all" type of thing. For the newbs who bought one. Although I would have to say, most owners, it seems, don't want to part with theirs. 
Their are some really great artists recording and sharing on here including you. I don't know If I could reach that level but 
