Personnaly I had two differents Jeff Rowland Model 1 amp before. I'm not absolutly sure but there could be 3 or 4 differents versions of this amp.
The first one is the one shown on the original advert on Jeff Rowland's website (the black and white picture). You can recognize it because it has only 2 small black caps between the 2 big ones. I've never seen this version in second hand and maybe Jeff never sold it like this (it could be a prototype version).
The second version (also the first Model 1 I've bought) was a little bit different than the first version because here you could find 3 small black caps between the 2 big ones.
This version was running really hot, you could not put your hand on it more that 5 seconds before you get burned. Most of V2 can't be turned to mono (even if the switch is there). About the sound... it was just pure even (no joke), an extremly warm and full sounding amp. I sold it and it was a mistake. This amp can be found with a serial before 1300 (something like this).
The third version of the Model 1 is just a different amp (serial over 1300). You can recognize it because it has 2 small grey Philps caps between the 2 big ones. It is more powerful than V2 and it really turns off when you turn it off (sound just cut, on the V2 it degrease slowly and stay on at a really low level all the time). But the V3 is just the shadow of the V2 for me. The sound is much much more common... nothing really special there. The amp doesn't run hot anymore, you can put your hand on it all the time, it's fine. No more warm sound, no more large power impression... just a classic sound from a classic amp. I had this amp after the V2... and I sold it without regret.
About the V4... well I'm not really sure it's a real version. The last units of the model 1 use a red circuit board like the Model 2 and 6, and not green like the previous versions. Hard to say if this is the only difference with the previous one...
That's all I know !! : )
