I need to decide.
I play experimental, hardcore, some punk, emo shiete.
I have built and love the jtm50 and it is more than loud enough....the only thing lacking is that bottom end for hardcore riffing and just straight up mean sounding drive.
let me be clear.....i am not looking for high gain metal sound, I like the raw tones of bands like Poison the well, refused and a bunch of bands that use plexi or early jcm800's (2203) I tend to not like the jcm800 tones.....but then again they may have been shiete jcm800's.

heres a link to a lame recording of my band
myspace.com/notinparis

anyways....opinions?

I am to considering building a Plexi, and am having difficulty decide on to 50 or the 100.  I'm leaning towards the 100, and running it on just 2 power valves.  I guess it would sound very similar to the 50 (although, ot is just a guess).

Running a 100-watt Plexi on two tubes is definite an option if you want more low end, which the larger iron at output will provide.  Obviously, you could gain the same benefit by just dropping a bigger OT on a 50-watter as well.  Output transformers don't care what their primary impedance are, they work on a ratio, so an 8000:8 output transformer does actually need at 8000 ohm primary impedance, it just coverts whatever it gets at a ratio of 1000:1, hence why we always have to compensate at the secondary.

Brett's concerns are mostly unfounded, and plenty of people run amps with tubes pulled all the time with satisfactory results.  However, the primary impedance at the OT isn't the only thing that will change though.  The plate voltages throughout the amp will be a little higher because you not longer have the resistance of those two power tubes.  This can mean higher headroom than expected and improper bias.  Rebiasing for the remaining tubes is definitely recommended.  But to be able to drop the voltages coming off the rectifier down, perhaps with a zener, would be another beneficial mod.  Honestly, if you can get the bias and voltages back in line, then the amp will work perfectly as 50-watt Marshall with a beefier tone. 

If you want to tweak your sound with more bottom end.....go to greytech sound.  Brian built me an awesome Plexi 50 with so much bottom tight sound, I sometimes have to roll off the Bass.  I think this sound you may be after requires MM power and output trannies....and the best power caps.  Hell, he even replaced the wire and upgarded every pot.  I have an amp with so much definition...it is not funny.  Once it broke in....I had the most natural sounding amp and if I want a heavy metal sound, it is there with the proper pedals.  But i assure you, this is not a heavy metal amp, it is a sollid rock and roll blues amp.

I think i have the best Plexi of them all, the only thing I did not do is the Soho caps.  Anyone, please tell me what that will do to my sound?  Take Care Happykamp