Cool thread; great sounding amps that really respond and feel like they have tubes.
These black and silver Studio Pro 112s were made between about 1996-2000 - production was moved to China in this time period. Earlier made in the US Studio Pros have a silver ring on the face of the knobs:
The Redline models came next and were produced until a few years ago:
The newest Bandits and Envoys have these sort of cosmetics:
I have a made in China black and silver and a redline Studio Pro 112 and much prefer the sound of the black and silver model; especially on the od channel. The redline has a deeper sounding reverb but is a much more brittle sounding amp IMO. I actually use both of them in a stereo rig; and they work well together. I haven't tried all the different Bandits and other Transtubes (except for the little Rage) so I can't really comment on them.