when I was using rack gear I would often run one of my rack preamps into the front end of my TwinReverb if I didn't have room on stage for the full rack and cabs and such...
I used to use a Peavey Rockmaster (high gain tube preamp) in front of a Roland Jazz Chorus. Talk about a firebreather!
My how times change.... 10 years ago, I was trying to get all the gain I could out of that Rockmaster with a 120watt amp, now I'm asking about 5watt Silverface Fenders