Falling on your topic while looking for informations about original Mig 50 schematics.
Though my english can be pretty bad, trying to help you may help me too.
These seem to be two reliable sources. Bruce Collins has a pretty good reputation, and it looks like Elan Portnoy used to be Director of Engineering at Sovtek around 1995. At least he said he was : https://www.harpamps.com/micKtubes/Sovtek-Midget.html
Let’s beleive both of them were genuine and told what they knew, I feel there are two reasons possible for these differences :
1- There are two main different MIG50. The first version without master pot (known to be very clean and difficult to make crunch, but maybe because of tubes choice), and an other one with master pot (known to be a growling beast, again, maybe because of different tubes). It could explain two different layouts, not only because these are two different beasts, but also because these two versions are some kind of top of the iceberg… there may have been several versions of these two main ones.
2- Sovtek isn’t known for having used stable sources of components. Don’t get me wrong, russian components can be very reliable (as much as they can be crappy… it depends what components). For instance during the cold war Russia was producing more reliable transistors than USA. Military grade was kind of the norm in USSR, and they produced components like crazy so it was pretty easy for Russian brands like Sovtek to get reliable components out of old Russian’s stocks. But Russian people are also known for being good at doing with what they got. It wouldn’t be surprising that if some ideal component wasn’t avaible during some weeks, but order still coming, Sovtek would have produce amps with component they had in stock. Even if values were different, cause “if it makes your windows shake while playing guitar, then it’s хорошо (good). Da !” Collins may just have correctly reported what he saw into an other MIG50.
So both layouts can be right, and your amp can be something else too, though still being a pure MIG 50…
IMO so many differences of components, while keeping people saying how good MIGs sound tells a lot about the quality of the design.
IMO again, if Portnoy may have had some reasons to not publish the real deal (copy protection), I don’t see why Collins would have fake his schematic. So I would prefer his layout anyway.
When it comes about EH giving the layout of their version of the MIG 50(no master copy), I would be very surprised (thought interested and grateful) if that would happen.
Which version of the MIG do you got ? With or without master pot ?