I stumbled upon a cheap Peavy Studio Pro 112 today, from what I've read, it seems to be a silver stripe transtube model with a "thrash" button instead of a "modern" switch. It's quite hard to find any info or sound clips of it because there's so many different models of the amp, so I'm wondering if anybody has any tips on identifying American/Chinese versions or anything about the sound of it?

If I remember correctly, the ones with the "thrash" switch are a newer generation, the knobs are parallel with the front of the amp rather than angled, and there is no red trim. The models with blue striping are pre-TransTube.

Does it look like this? http://www.jarek668.yc.cz/soubory/peavey.JPG

I haven't played that generation of this amp much, but it should be good, regardless of being American or Chinese made. Check the back of the amplifier part itself, it'll say either "Made in USA/China".

If you want to see if it sounds good, select the lead channel, push the thrash knob in, and use the following settings:
Pre-gain: ~6
Post-gain: ~6
Low: ~6
Mid: ~4
High: 8-10
I forget what position you want the "gain" button on for these, try both. One should be good, the other will either be too chunky/muddy, or too low gain.

If it sounds good, then you found yourself a good amp. If it doesn't sound good, it's broken, though I've never seen one of these break

That's definitely it! Cheers man! While I'm at it, I'm guessing the two inputs just add different amounts of gain?

Yeah, it's basically a preamp (you should read the manual on these, they're fascinating if you're a nerd). Passive pickups go to hi (+6db IIRC) and Active or really high gain pickups go to lo (no gain).

So it's like the odd bass amp then? Hoping it has the manual and the footswitch, but it's in a pawnshop. Always something that has to be done with gear from those places. Still, £80 is a lot cheaper than most crappy amps in the UK, win either way.

An odd bass amp? It's like a Peavey guitar amp! Most 5150s and 6505s have separate high/normal gain inputs, though the + models with extra channel don't IIRC.

Aye, well a lotta bass amps have the active/passive inpts. I've only ever seen two Peavy amps in my life, guitar shops in Glasgow are mostly just full of Marshall, Vox, Fender, ect.