I recently got a Mig-50H in a trade. Previous owner knew very little about it, had it as a project he never finished. When I popped it open, I noticed a few things. 1) Someone replaced the heater wiring, including disconnecting the elevated heater voltage winding for V1 and replaced with standard 6.3v daisy chain. 2) Output jacks have been changed out for standard mono jacks and there is a shielded lead that comes under the board that is connected to the board next to the bridge rectifier that is detached. It's my assumption that this is the NFB lead that connects to the tip of the 8ohm output on the schematic but I am having a hard time finding good reference pics online. The one's I can find all vary slightly and frankly the schematic I have isn't great quality either. Other than that, the build quality seems solid, tubes test good, all the voltages seem ok but I can't seem to trace an input signal any further than the plate on V1a. It seemed unlikely that it would be because of the heater supply but then again I'm not sure why it was designed that way in the first place so I am a little stuck and hoping someone has had a few of these on their bench and can chime in.