Kev999
I'll just throw in a couple of alternative ideas. Instead of mic'ing, you could take a direct feed from the amplifier's preamp out or effect send (if it has this). Then, after the part has been recorded, you could play it back routed through the amp and use a mic to record some room ambience.

Interesting idea! Since I have a DI on my amp, I hadn't considered the effects loop. Gotta be line level. I need to check.
 
Ideas like this make me glad I got a US-16x08 instead of a US-4x4!
 
Should I ever choose to accept that mission, of course. 

using effects loops or direct outs of amps for recording,
especially guitar amps,
ESPECIALLY rock guitar amps,
sound of pure sh!te.
 
always.
 
kill with extreme prejudice.
 
or sumptin'

But that my favorite brew: Miller Sh!te. Whaddami gonna do? 

suck it down, and move forward!!!
 
LOL
 

i have experimented for years with all this stuff..
 
 
i end up with a very simple solution:
 

 
even tho it does not show it connected in this shot, i've got my palmer PDI-09 on top, with the amp output going directly into it, and back out and into the speaker cab.,,
the palmer gives me line level out with XLR, that goes directly to the mic preamp......and control over simulated cabs (eq filter, not digital sim of course, all passive)
 
then i have a shure ksm44 on the speaker.. thru the mic preamp and into the soundcard.....
 
i mix these two together into one track.
 
typically, the amount of direct Palmer signal versus mic is about 75% to 25% mix.
the direct is so good....
that it cannot be bested by the mic.
 
but the mic picks up room sound, transients that are not in the direct,
so for me, this is my best practice.
 
a lot of times, when i want a track to sound very dry and in your face,
i simply toss the mic track away.