I've had my (self built) OTS for a few months now.  Originally put in MESA power tubes 'cause they were about the cheapest.  Figured they'd be good enough for the break-in period.
The amp sounded pretty good, but not as good as the UTube samples that persuaded me to buy it.

The other day, I bought some JJ's as I needed a set for backup.   Put the JJ's in, and WOW!
They were only $5 or so more than the MESA's but now the amp's sounding great.
With the MESA's, when playing distorted chords, it got downright ugly at times - harsh, lots of odd harmonics.  With the JJ's, I instantly noticed the tone was much thicker and smoother. Now those distorted chords ring like they're supposed to.
Maybe with some esoteric NOS/VOS tubes it might get even better, but for now I'm quite happy.

I have to agree with those who say this amp is like no other.  If you have one and aren't happy with the tone, stick with it and try some different tubes or mods or speakers.  You'll most likely eventually get what your looking for.  Its taken me months of gigging and tweaking to get myself into the ballpark. Don't give up!

I did some tube rolling on while i was stuck at home last week.(had the flu and work forbids me to go if i have it) After two solid days i came to realize that the Telefunken ribbed plate in V1 was almost too good. It was very "hi-fi" for lack of a better word and too bright. The JJ in V2 was very nice on lead sections but a bit too chunky on rhythm parts. The TAD 6L6WGC-STR's were a bit too loose in the bass and bit too scooped. The Tung-Sol 6L6GC reissues were ok, but a little to intense in the Low end.

It was beginning to sound like Goldilocks

I pulled the Telefunken out of V1 and put the ANOS GE Long Plate 12AX7 back in, pulled the JJ out of V2 and put the JAN GE 5751 back in, and put a new set of JAN Phillips 6L6WGB's in V4 & V5 (the JAN 6L6WGB's i had before were the last of a stash i had bought a few years ago and ran biased very hot in the BM for the heck of it for two weeks and could never get to bias low enough to run properly again at full B+ voltage). I biased to 70%, set the OD trim to 1 o'clock and wowsers. I think i found the magic bullet for HRM Bypassed Bluesmasters.

Clean sounds can range from Tweed Bassman/Early Marshall cleans to as it was designed to be, or Blackface cleans if you lower the mids down to about 9 o' clock or even cut them out completely. They are very nice and warm and bright without being muddy or brittle. Very Nice. Turn the preamp up to 8 or higher on the clean side, turn up the clean master and you will have a fat natural overdrive sound that is full and nasty! (in a good way)

OD sounds are unreal. It can range from sounded like a cranked tweed deluxe, cranked blackface bassman, a boosted blackface deluxe, to total hot rodded fender deluxe overdriven, to chunky Plexi depending on how you set the Drive, OD Trim and work your guitars controls. The 5751 seems to shape the tone in a way that the 12AX7 doesn't, making the lows less flabby, the mids nice and fat, and trims just enough highs to make it not overly bright. I have taken my Tube Screamer and Fulltone out of my chain and just keep my Fuzz pedals in the chain now if i decide i want more of a fuzz sound than a straight OD sound.

Of course, the HRM tonestack can do this as well, but it does make it sound more like a Hot Rodded Marshall Plexi (to me) than a Hot Fender, and the tone difference from clean to drive was just too much for me. Plus, the clean and OD channels sound more identical since they are using the same tone stack, and the PAB can be used as an boost instead of just bypassing the main tonestack so that the HRM stack is the only stack in use, which is the only way to really use the HRM stack properly (both tonestacks=Mud)

So there ya go. My .02 cents on how to get some rockin tones from an HRM Bypassed Bluesmaster.I think my tweaking days are over for now on this amp. All i need now is a way to record some soundclips, which i have been dying to do for a while now.

Hope this helps!

Gregg