to get the good tone out of a good tube amp you need to drive the power section wich means turning it up..way up.
If volume is an issue power attenuators such as the thd hot brake allow you to crank the amp driving the tubes yet hear it at a lower volume.
Though even with this it wont give the full effect of your speakers being driven. when i say speakers driven i'm thinkin like celestion vintage 3os
the greatest tones ive ever heard came from amps like the marshall blue braker, plexi,ac 30 or fender twin cranked(though a twin sounds good at any volume imho)
To really get a good tone it gets complicated though you have to consult voodoo guru's and scour the earth for that "magic" one of a kind sounding amp then figure wich speakers and pickups on your axe compliment it not to mention throwing a distortion box like the rat or tube screamer in front of it and an e.q. stomp.Even then the way an amp sounds isnt consistant, on different days it will behave differently.
just crank it up till you get the good tone but not so much that you get the muddy tone.then, take your sm-57 and move it around the room and see for yourself what you like.If you could get a second sm-57 that would help a lot as well. Then you could put one about a half a foot from the ampo and the other somewhere further back.
As someone who's not a professional engineer I'd say youll need to find your sound through trial and error. But turn it up loud and put 2 sm-57s on it-personally I dont always put my mics right up on the amp i like to mess around with mic placement. It depends on the sound your amp produces with the room and the mic and what sound youd want etc etc etc...............A real pain in the ass or a fun adventure....
Oh, and if your in a basement doing this consider the power attenuator.It would be a shame to catch a case of tinnitus.
A lot of cats will use 20 or even 15 watt amps in the studio, allowing them to get a cranked sound at reasonable volume, though with a power attenuator you can acheive the same thing
